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Concourse 2

Ambiguity

escher

This is quite a long guide with separate sections, not necessarily connected or following on from each other.
If you are here for the first time, and just want to get an overview of the scope of ambiguity and the various classifications we can use, work through it sequentially but if you are returning to check something, here's a list of the contents to take you to its various sections.
Links in bold are to major sections, others lead to subsections.
Clicking on -top- at the end of each section will bring you back to this menu.

Sources of ambiguity Lexical ambiguity modal auxiliaries adjectives classifiers comparative and superlative Syntactical ambiguity
-ing forms other -ing forms adverb modification conjunctions clause constituents Semantic ambiguity genitives
negation theme and rheme case adjuncts, conjuncts, disjuncts limiters Pragmatic ambiguity Summary

Ambiguity is not, of course, a phenomenon which is confined to English.  All languages can be used in a way that allows two possible interpretations, sometimes more, of what seems to be a simple enough statement or question.
In English, for example, the following has recently occurred:

He: Welcome home.  I've saved you a job.
She: Thanks, that's good of you.
He: Don't be sarcastic.
She: What?!

think Task:
What has gone wrong?
Think for a minute and then click here.

Many of the examples below are culled from other guides on this site in which ambiguity is considered almost in passing.  Here, it is the focus.

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source

Sources of ambiguity

This guide considers three main possible sources of ambiguity, explains what the problem is and tries to suggest some ways to remove the ambiguity.  The three are:

  1. Lexical ambiguity
    The source for this is the fact that some words have homonyms which look and sound the same but carry different meaning.
    In spoken language, homophones will have the same issues and in written language homographs may also be a source of ambiguity.
    The issue we saw above with the word save is not, however, to do with homonymy; it concerns polysemy, the phenomenon of words have different but connected meanings rather than different and unconnected meanings.  The borderline between homonyms and polysemes is, however, somewhat blurred.
    There is a guide to the polysemy, linked below in the list of related guides at the end.
    Here are some examples of what is meant:
    Issue Example Meaning 1. Meaning 2.
    homonymy They found the quarry They found the animal they were hunting They found the source of building stone
    polysemy What did you read last year? What did you study at university? What reading did you do last year?
    He may come He has permission to come It is possible he will come
    grey area She took a taxi She used a taxi as transport She stole a taxi
    homophony The border / boarder is here The edge / frontier is here The paying guest / tenant is here
    homography He bought a new bow He bought a new violin accessory He bought a device for shooting arrows
    It is unlikely that any of these examples set in context, will produce a great deal of ambiguity, of course, but, standing alone, they cannot be disambiguated.
  2. Syntactical ambiguity
    There are a number of ways ambiguity can arise from the syntax of a sentence or clause and they are mostly to do with what modifies what or what qualifies as an independent component of a sentence or clause (related areas as we shall see).
    They can also be to do with how tense forms in English are understood and how subordination and coordination are understood.
    Here are some examples:
    Issue Example Meaning 1. Meaning 2.
    modification I said I would come on Monday I said this on Monday I will come on Monday
    Being honest, he was seen as rude My honest opinion is he was seen as rude Because he was honest he was seen as rude
    independence I washed the car in the corner I washed the car which was in the corner It was in the corner that I washed the car
    I spoke to the man in my office I spoke to the man who was in my office It was in my office that I spoke to the man
    tense form I'm driving to London this week Sometime this week I will drive to London It is my temporary habit to drive to London
    The professor is writing to the students The professor is currently writing The professor intends to write
    conjunction She was exhausted but Mary worked on Mary and she are the same person Mary and she are different people
    Syntactical ambiguity arises from the phenomenon of syntactical homonymy and can sometimes be almost impossible to untangle without reconstructing the clause or sentence.
  3. Semantic ambiguity
    Some see this as a subset of syntactical ambiguity but it is noticeably different because much depends on the shared knowledge and speaker perception rather than simply the syntax.  It concerns what is meant, not what is necessarily understood by decoding the syntax.
    Here are some examples:
    Issue Example Meaning 1. Meaning 2.
    who does? John and Peter have a house in London John and Peter share a house in London John and Peter have separate houses in London
    what is the object? John used his own car and so did Mary Mary and John used John's car Mary and John used their own cars
    limitation The tiger is a dangerous animal This particular tiger is dangerous Tigers are dangerous
    what is the subject? John saw the boss and he asked him to wait John asked the boss to wait The boss asked John to wait
    The last example is called by some anaphoric ambiguity because it is impossible to know which referent is appropriate for he.

At the end we will also consider a fourth source of ambiguity which is not dependent on language use but which stems from social and cultural sources.

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words

Lexical ambiguity

It is quite rare for a lot of polysemes and homonyms, especially those concerning content words, to cause a great deal of difficulty because the context almost always determines the meaning that is meant.
We are unlikely to misinterpret, for example:
    I took an aspirin
as
    I stole an aspirin
or
    She dug the garden
as
    She appreciated the garden
although misunderstanding is always possible if the context is too thin.

Function words and auxiliary verbs are a very different matter because the meaning they convey relies on the co-text.
Here are some examples but no guide to ambiguity can ever cover all the possible sources.

will

will and other modal auxiliary verbs

Will you marry me?
Well, will she?
 

The verb will is polysemous because it applies to a future time in one sense and to a current willingness in another.  So,
    Will you marry me?
concerns the woman's current willingness to commit to something, but
    Will she marry him?
is a question requiring speculation about the future.
In the first example, the modal auxiliary verb refers to dynamic modality (volition) and in the second to epistemic modality (propositional truth).
That is the reason that will can appear in both parts of a conditional sentence such as:
    I will give you a lift if you will share the petrol costs
Normally, the rule is not to use will in both clauses but it is correct here because the first incidence of will refers to the future and the second refers to the hearer's willingness to do something.
It is only useful to tell learners that we cannot use will in both parts of a conditional sentence if we are clearly using the verb in one of its main meanings.  In other words, being careful to avoid ambiguity.

A fundamental reason why modal auxiliary verbs cause so much trouble for learners is their polysemous nature.
Here are some examples of what is meant:

Verb Example Meaning 1. Meaning 2.
might She said they might ask questions at the end She gave them permission to ask questions She thought it was possible they would ask questions
may They may go They have permission to go They might go
He may not come I will allow him not to come He might not come
can Can you help her with her homework? Please help her with her homework Are you able to help her with her homework?
You can talk to him I give you permission to talk to him He is approachable
†I can not smoke I have the ability not to smoke I am not allowed to smoke
would He would be rude to his mother if she asked a question He was habitually rude to his mother when she asked a question If his mother asks a question his response is likely to be rude
could She could explain it more clearly She was able to explain it more clearly She should explain it more clearly
It could bend It has a flexible nature / ability It is possible that it will bend
I could have left it with John John gave me permission to leave it with him It is possible that I left it with John
If you come late you could miss the speeches It is possible you will miss the speeches You will be able to miss the speeches
ought He ought to be there I expect he is there He has an obligation to be there
must He must be at home I am certain he is at home He is obliged to be at home
have to He has to be at home
† This ambiguity cannot occur in writing because can and not are written separately in Meaning 1.

The moral is that all modal auxiliary verbs have the possibility to be interpreted in multiple ways.
Elsewhere on the site, the verb could is shown to have eight possible meanings (present possibility, future possibility, past possibility, present ability, future ability, past ability, permission, complaint), might has six (present possibility, future possibility, past possibility, suggestion, permission, complaint) and even should has four (advice, obligation, conditional uses, logical deduction).
Other modal auxiliary verbs, especially the central nine, suffer from the same ambiguity of modality type.

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learners

adjectives

The hardworking students passed  

Scope
radio

This sentence:
    The hardworking students passed the examination
is ambiguous because this may mean either:
    The students who worked hard passed the examination
    (and other students, less hardworking, did not)
or
    The students, who worked hard, passed the examination
    (all of them were hardworking and all of them passed)
Other adjectives are open to similar multiple interpretations.  For example:
    The available money is inadequate
in which the adjective available can mean:
    all the money (with no more to come)
    the money available now (with more to come)
This can be disambiguated in two ways:

  1. By making a relative pronoun clause and distinguishing between defining (restrictive) and non-defining (unrestricted) forms:
        The money, which is available, is inadequate
    (i.e., it is all available)
    vs.
        The money which is available is inadequate
    (i.e., only the money which is available, not all of it)
  2. By postpositioning the adjective:
        The available money
        all of it
    vs.
        The money available now
        some of it with more to come

The second disambiguation trick works with other adjectives as in:
    The visible stars
    The stars visible tonight
    The present staff
    The staff present now
The first refers to all the visible stars, the second to only those visible tonight, the third to the entire staff at the moment and the fourth to only those employees who are here.

Determining how an adjective should be understood in the sense of what is included and what excluded is not always simple.  It is not that we have a polysemous word acting as an adjective (although that happens) but where the scope of modification starts and stops.

The adjective bad is somewhat ambiguous in this respect.  For example:
    She felt bad
could imply that she felt unwell or that she felt guilty although this can be disambiguated with the use of the adverb so:
    She felt badly
can only mean unhappy or guilty, not unwell.

Classifiers, epithets and punctuation
class

There is some ambiguity in written language whether a word is intended as an adjective (an epithet) or a classifier because:
    a senior school teacher
could be interpreted as
    a teacher at any type of school who is experienced and older
or
    a teacher who happens to work in a senior school
In the former, the word is adjectival and in the latter it is a classifier.

Commas are often optional but required when there is possible ambiguity.  For example:
    It's a large house plant
is unlikely to be misunderstood as a plant only for use in large houses but to avoid any ambiguity, it can be written as
    It's a large, house plant
Compare:
    It's a small garden plant
in which there is ambiguity which can be eradicated by punctuating it as
    It's a small, garden plant
or
    It's a small-garden plant

old and new: inherent and non-inherent meanings
car

The adjective old may be applied to inanimate and animate nouns but when it is applied to animate nouns the meaning will vary depending on how it is used (attributively or predicatively).  So, for example:
    He is an old friend
will be understood non-inherently as applying to a long-lasting friendship, not to the person but
    My friend is old
will be understood as applying to the friend, not the friendship.
Unfortunately the word old has two common antonyms: new and young and they are differently understood depending on the nature of the noun to which they are applied.
So, for example:
    She's a new friend
and
    All these students are new
will not be seen as applying to the people but to their recent arrival whereas
    She's a young friend
or
    The students are young
can only be understood as applying to the people directly.
However:
    There's a new car in the car park
and
    That car in the car park is new
are truly ambiguous and could mean
    The car has only recently appeared in the car park
or
    The car has recently been manufactured
and only context can disambiguate the meaning.

A further, connected source of ambiguity lies in the fact that some adjectives can apply to a person and to a relationship so, for example, while it is clear that:
    She's a new friend
    They are old rivals

both apply to the friendship and the rivalry, not the people involved, it is less clear whether the adjectives in
    He's a reliable friend
    She's a remarkable friend
refer to a reliable / remarkable person or a reliable / remarkable friendship.
Ambiguity can be avoided by using the adjective predicatively because then the assumption will always be that it applies to the person:
    My friend is reliable
    Her friend is remarkable

Comparative forms
2

The question here is whether the words more and less are acting as adverbs modifying adjectives or as determiners modifying noun phrases.  It matters because the meaning changes depending on the grammatical function of the word.  In that sense, this straddles the boundary line between lexical and syntactical ambiguity.
Here are three examples:

  1. They provided more accurate figures
    1.     = They provided more figures which were as accurate as the old ones
      or
    2.     = They provided figures which were more accurate than the old ones
  2. I want more useful work from you
    1.     = I want more work from you which is as useful as the work you have done
      or
    2.     = I want work from you which is more useful than the work you have done
  3. She had less expensive work done
    1.     = She had less work done which was as expensive as the previous work
      or
    2.     = She had work done which was not as expensive as the previous work

The ambiguity arises from the fact that in:
i.a., ii.a. and iii.a., the words more and less are determiners referring to the noun phrases accurate figures, useful work and expensive work
but in:
i.b., ii.b. and iii.b., the words more and less are adverbs modifying the adjectives accurate, useful and expensive

It is impossible to tell by looking at the sentences what the words more and less are doing grammatically.  Rephrasing as above will remove the ambiguity.

Superlative forms
Mountaineer, Mountain, Peak, Man, Climbing, Climber

Compare
    The girl is most intelligent
and
    The most intelligent girl
both of which are possibly ambiguous because they can mean either:
    The very intelligent girl
or
    The girl who is more intelligent than the all the others
The use of the definite article determiner can disambiguate this because
    The most intelligent girl
will only be understood in the second sense.
The key here is not to word class because in all the examples, the word most is an adverb modifying the adjective.  However, the word is polysemous because is means very or extremely and it forms the superlative of an adjective expressing the uppermost degree.

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switch

Syntactical ambiguity

Much of syntactical ambiguity arises from the possibility of, so to speak, throwing a mental switch to decide which line to take.
Tense forms in English, or most languages, do not have a one-to-one relationship with time.  We use, therefore, present and past tenses to talk about the future, past tenses to talk about the present and so on.
There is a good deal more about this in the guides to time, tense and aspect, linked below, so some examples of the possible ambiguities will be enough here.

driving

-ing forms

He's driving  

At first sight, a sentences such as:
    He's driving
is not ambiguous, especially when it's linked to an image as here.
However it can mean:

This is where we encounter a famous Chomskyan concept.  Chomsky, to whom there is a guide linked at the end, chose to demonstrate what he meant by deep structure with the example sentence:
    Visiting aunts can be boring
because that can mean:
    Aunts who visit can be boring
or
    The activity of paying a visit to aunts can be boring

It is, in fact a bit of a four-way cheat in our terms here because the ambiguity relies on:

  1. Selecting a transitive verb so that there is manufactured ambiguity concerning subjects and objects.  You cannot, for example, construct a similarly ambiguous sentence with verbs like arrive or speak because you get the unambiguous:
        Speaking clocks can be irritating
  2. Selecting a semantically allowable transitive verb.  You cannot, for example, construct a similarly ambiguous sentence with verbs like explain or show because you get the unambiguous:
        Showing your anger can be inadvisable
  3. Using the uninflected modal auxiliary verb, can, to disguise the verb-noun concord.  You cannot, for example, construct a similarly ambiguous sentence without the modal auxiliary because that produces:
        Visiting aunts bore me
        Visiting aunts bores me

    which contain no ambiguity because the first has a plural noun as the subject and the second has a singular gerund as the subject.  We don't need to think about deep structure to disambiguate the sentences, simply leaving out the modal auxiliary verb will do.
  4. Selecting a verb which has a gerund form (a verbal noun) and a participle form which can act as an adjective.  You cannot, for example, construct a similarly ambiguous sentence with verbs like wear or repair because neither wearing nor repairing can operate as participle adjectives although the verbs are transitive.  We allow:
        Wearing warm clothes can be useful
        Repairing computers needs some care
    but not:
        *These are wearing clothes
        *He is a repairing man

It is quite difficult to make a parallel sentence to the one Chomsky used although:
    Eating apples can be healthy
    Drinking water can be good
    Cleaning materials may be expensive
    Burning rubbish could be dangerous

and just possibly
    Climbing plants can be dangerous
(if you are a field mouse)
will show the same kind of ambiguity.
The parlour game is to think of ten more.

In fairness, this was not the point that Chomsky was making.
He used ambiguity as a way of revealing the inadequacies of a structuralist approach to grammatical analysis and was not concerned with communicative effect.

Tense-form ambiguity is a much more important issue for teaching.

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infinite

Other non-finite -ing forms

Misuse of the -ing participle in non-finite clauses often results in what is called a dangling or unattached participle.  For example:
    Getting on the bus, John's wallet fell from his pocket
is semantically and grammatically flawed because it was not the wallet that got on the bus.  To avoid this kind of ambiguity, the participle and the main clause verb need to have the same subject.  The use of a finite clause solves the issue:
    While he was getting on the bus, John's wallet fell from his pocket
In this case, little ambiguity is caused because we know that wallets do not, of their own volition, take public transport.

However, there are times when the rule is not quite so clear cut.  For example:
    I saw Mary getting off the bus
is likely to be interpreted as:
    I saw Mary while she was getting off the bus
but could mean:
    While I was getting off the bus, I saw Mary
We need to be more careful here because both the possible subjects are able to take public transport.
In order to repair the ambiguity, we have to rephrase the sentence as:
    I saw Mary when she was getting off the bus
or
    I saw Mary when I was getting off the bus

The rule of attachment to the same subject is often relaxed so we allow:
    Being Friday, the staff left early
which is not ambiguous because the staff cannot be Friday.
On the other hand,
    Being optimistic, Mary will be able to do the job
is ambiguous depending on whether the speaker or Mary is the optimist.
The ambiguity here is explained a little more (and a little more clearly) below, under semantic ambiguity.

These sorts of non-finite clauses used to express temporal or causal relationships can give rise to some ambiguity of meaning.
For example:
    Being in New York, she went to see him
could mean:
    While she was in New York, she went to see him
or
    Because she was in New York, she went to see him.

In all such cases, rephrasing the thought using finite rather than non-finite verb forms solves the problem as can using the right subordinating conjunction as in the examples of meaning above.

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hurry

Adverb modification

He quickly got lunch  

It is often difficult to determine which verb an adverb modifies when there are two in the same sentence.  For example:
    The people who came quickly got lunch
has two interpretations depending on which verb is being modified by quickly:

  1. The modified verb phrase is came, in which case we have:
        People who were quick to arrive got lunch
  2. The modification belongs with the verb got, in which case we have:
        The people who came got lunch quickly

We can re-phrase this to remove the ambiguity as we have done here.  The key is to put the adverb in the right place.
It can also be disambiguated by pausing in speech after quickly (and signalling sense 1.) or after came (and signalling sense 2.).
That is straightforward with middle-position adverbs such as those of manner which are mobile but even easier with adverbs of indefinite frequency as in, e.g.:
    The men who arrived late frequently missed lunch
vs.
    The men who frequently arrived late missed lunch
because these adverbs conventionally precede the main verb.

There are also times when it is not clear whether an adverbial is functioning to modify a verb or its subject or object.
For example, in:
    His friends at that time were working
could mean:

  1. His friends were working at that time
    which modifies the verb phrase, or
  2. The friends he had at that time were working
    which modifies the noun phrase

and unless we know whether the prepositional phrase is modifying the noun or the verb phrase, we cannot arrive at the meaning.  This is an example, arguably of phrase constituent ambiguity, which is considered in much more detail later.  The concepts of syntactical and phrase-constituent ambiguity overlap with blurred edges.
Simple re-phrasing (as above) will disambiguate the meanings.

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link

Conjunctions

Some conjunctions cause ambiguity issues.

although and while

Both although and while are subordinating conjunction of concession and occur unambiguously in, for example:
    I like reading in the evening while my husband prefers watching TV
    Although I like reading in the evening, my husband prefers watching TV
etc.

A little care is needed, however, because while is also a temporal subordinator so, for example:
    Although it is raining, I'll take a walk
is unambiguous because although has only one function but
    While it is raining, I'll take a walk
can mean:
    Although it is raining I'll take a walk
or
    As long as it is raining I'll take a walk
It could also mean:
    Because it is raining I'll take a walk
because while sometimes carries the sense of causality usually signalled by so or because.

but and although

There is also scope for ambiguity with the distinction between coordinators and subordinators.
In coordinated clauses we can omit the subject, providing it is common to both clauses so we get, for example:
    Mary was exhausted but worked on till six
in which it is clear that Mary is the subject of both clauses.
We cannot do this with subordination so we do not allow:
    *Although Mary was very tired, worked on till six

There is, however, a little more to it than that because in a sentence such as:
    He was exhausted but John worked on till six
it is averred by some that He and John must refer to different people.  In other words, He cannot be a cataphoric reference to John in a coordinated sentence.  This is somewhat questionable and the sentence is at best ambiguous insofar as He and John could refer to the same person or to different people depending on context and co-text.
With subordination, on the other hand, cataphoric reference is assumed so in:
    Although he was exhausted, John worked on till six
it is inevitable that he and John will be assumed to be the same person.

so and so that: purpose or result?

The conjunction so also causes problems because it implies both a result and a cause.
It is resultative in, for example:
    The night was very clear so I could see the ships out to sea
It is causative in, for example:
    I dug a deep hole so the tree was firmly planted
However, ambiguity can arise with a sentence such as:
    Someone stole my car so I couldn't get to work
which means either:

  1. The result of the theft of my car was that I couldn't get to work
    or
  2. Someone stole my car to prevent me getting to work

The way to disambiguate is to replace so with because when we are referring to result and then we get:
    Because someone had stolen my car I couldn't get to work
which is unambiguous, or to rephrase the thought as in b.

The same consideration applies to the coordinator so that.  It is resultative in:
    The ground was icy so that I was careful how I walked
in which the care is a result of the ice and so that is acting as a coordinating conjunction.
It is, however, purposive and a subordinating conjunction in:
    I put salt on the driveway so that the ice would melt

This means that, e.g.:
    He was standing in the light so that I could see him
is ambiguous and means either:

  1. The result of his standing in the light was to make him visible
    (coordinating the clauses)
    or
  2. He stood in the light in order to make himself visible
    (subordinating the second clause to the first)

Again, we have to rephrase to exclude the possibility of ambiguity.

before

Temporal conjunctions can also cause ambiguity if handled carelessly.  For example:
    I expected he would be happy with the figures before the meeting started
can be interpreted either as:

  1. Before the meeting started, I expected he would be happy with the figures
    or
  2. That he would be happy with the figures before the meeting started was what I expected

The ambiguity can be resolved by moving the temporal clause to the initial position as in a.

if and when

The conjunctions if and when also cause problems.  In, for example:
    When possible, the work should be completed without disturbing the residents
has two interpretations:

  1. Whenever it is possible, the work should be completed without disturbing the residents
    or
  2. If it is possible, the work should be completed without disturbing the residents

Resolving the ambiguity simply means being careful to use if when a conditional rather than temporal meaning is intended.

if and whether

Consider:
    Tell me if you need any help
which has two interpretations:

  1. Tell me if you need any help
    as a true conditional in which the imperative depends on the need for help
    or
  2. Tell me whether you need any help
    which is not conditional and simply asks for the speaker to be informed

Disambiguation again involves using if only in conditional senses.

because

Some ambiguity may arise with negative causality so, for example:
    I didn't come because of the chance that she would be there
may be interpreted either as:

  1. The reason I didn't come was because there was a chance she would be there
    or
  2. The reason I came was not that there was a chance that she would be there

Only context and intonation (stressing because) will disambiguate the meaning unless we rephrase the whole meaning as:
    There was a chance she would be there so I didn't come
and
    That there was a chance she would be there was not the reason I came.
This is also considered below when we come to the ambiguity that negative sentences can evince.

to and in order to

The preposition to is sometimes just an abbreviation of in order to.
This can create some ambiguity.
Compare for example:

In the first case, we have a to-infinitive doing its usual catenative job referring to a prospective event.
In the second case, however, to is an abbreviation of in order to and is not catenative.
Here's a slightly different example:

is ambiguous because it means either:

and only rephrasing such as above can disambiguate the sentence.

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ingredients

Clause constituents

This is a major area of ambiguity and the final one to tackle under syntactic ambiguity.
There is a dedicated guide to disentangling clause constituents on this site, linked below, so here we will rely on a few examples of the sorts of ambiguity that can arise.
Here are the examples:

Instrumental phrases

Many case-grammar languages have a way of marking instrumental case but English doesn't, preferring to rely on prepositional phrases.  Unfortunately, prepositions themselves are polysemous.  The preposition with carries the meaning of an instrument as in:
    I cut down the tree with an axe
and of accompaniment as in:
    The man in the corner with the dog.
This causes problems.

For example:
    Anne hit the intruder with a chair
is probably not ambiguous at all (but it is conceivable that the intruder was carrying a chair).
    Anne shot the intruder with a knife
is also unambiguous because you can't shoot someone with a knife so the only interpretation is that the intruder carried the knife.
However,
    Anne hit the intruder with a gun
is truly ambiguous because it can be interpreted as either:

  1. Anne used a gun to hit the intruder
    or
  2. Anne hit the intruder who was carrying a gun

So rephrasing is necessary to make the sense clear.

Prepositional phrases as modifiers of nouns or verbs

Take:
    I shouted to the man by the river
which has two interpretations:

  1. By the river I shouted to the man
    or
    It was by the river that I shouted to the man
  2. I shouted to the man who was by the river
    or
    It was the man by the river that I shouted to

It depends on whether we consider by the river to be an independent phrase or one which is attached to the noun.
The subject of the sentence is clear: it is I.
The object, however, can either be:

  1. the man by the river
    or
  2. the man

The adverbial phrase which modifies the verb is then absent (if a. is the object) or is by the river if b. is the object.
In other words, we have to decide whether the shouting happened by the river or not.
We can use a diagram to make it clear:
river

In the first case the verb phrase in blue has the blue adverbial modifying it with the verb's object in red.  The phrase by the river is independent and can be moved to the beginning to get:
    By the river I shouted to the man
In the second case the verb phrase is unmodified and the object is in red but by the river is not an independent phrase because we cannot move it to the beginning and retain the same sense.

Here are some more examples taken from various guides on this site for you to untangle:

Disambiguation in writing

In written language, it is impossible to disentangle independent and mobile phrases so rephrasing is the option.  This often means:

  1. Moving the prepositional phrase:
        At his office he used the computer
  2. Making a cleft sentence:
        It was the boy in room 13 that the teacher shouted at
  3. Otherwise defining the object:
        He cut up the corner tree
  4. Making a passive:
        The tree in the corner was cut up
  5. Using a relative pronoun clause:
        John upset the lady who was in the garden
  6. Changing the prepositions and producing, e.g.:
        He read the book about the island

Disambiguation in speaking

In speaking we can deliberately move the tonic syllable to disambiguate what might otherwise be unclear.  For example, the sentence:

Anne hit the man with the chair

has two possible interpretations as we saw.

We can disambiguate this in speaking by paying attention to how the utterance is stressed.  Like this:

1 Anne hit the MAN with a chair
pre-head head nucleus tail
2 Anne hit the man with a CHAIR  
pre-head head nucleus -

In case 1, the pitch movement is most obvious on the word man so that becomes the focus of attention.
In case 2, chair is the focus because that is where the pitch movement occurs.
Disambiguating which meaning is intended by pausing and tone shifts are what Wells refers to as the demarcative function of intonation, i.e., the separating off of the crucial data.

Position and direction adjuncts

The usual rule in English is that position adjuncts cannot co-occur with dynamic verbs of motion but directional adjuncts of place can so we do not allow:
    *He is climbing at the top
but we do allow
    He is climbing to the top
and
    He is sitting at the top
An ambiguity can arise, therefore, concerning whether, for example:
    The children were running outside
means:
    When the children were outside, they were running
or
    The children were in the process of moving from inside to outside
Usually, the assumption will be that direction of movement is the intended message but that is not always the case.
Because some prepositional adjuncts are always directional, the ambiguity cannot arise, for example, with:
    I'm going to walk into the garden
but can with the preposition in and outside which refer to both direction and position so
    He walked in the airport
might mean he did some walking in the airport or that he moved into the airport on foot and
    They threw it outside the house
might mean they threw it from inside to outside or that it was outside the house before they threw it.
The former is what people will usually understand.

yes-no questions

Nearly all yes-no questions are, by their nature ambiguous in terms of what they are asking.  Really simple questions such as:
    Is John here?
are not ambiguous because the direction of the question can only be John's presence or absence.
However, a question such as:
    Did Mary cook the turkey last night?
contain four phrase elements (the subject, the verb phrase, the object and the adverbial of time).  It means, therefore, that a yes-no question could be directed at any of these constituents.  Like this:
    Was it Mary who cooked the turkey last night?
    Was it last night that Mary cooked the turkey?
    Was it the turkey that Mary cooked last night?
    What did Mary do to the turkey last night?

and only the co-text and context can disambiguate this in writing although sentence stress can make the sense clear in spoken language by stressing Mary, last night, the turkey and do respectively.
The disambiguation which the cleft forms allows is, incidentally, one of the motivations for their use although, as we see from the fourth question, the verb cannot be the focus of a cleft sentence form and the question is differently formed.  We cannot allow:
    *Was it cook that Mary did to the turkey last night?
There is more on cleft sentences in the guide to them, linked below.

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talk

Semantic ambiguity

Now we come to semantic ambiguity caused mostly by the hearer's inability to understand what belongs to what in the utterance.

shed

Genitives

the gardener's shed  

The genitive in English does more than refer to possession and therein lies a good deal of scope for ambiguity.

In the example above of the shed, for example, it is unclear whether the reference is to:

  1. a particular gardener's workplace (association)
  2. a shed owned by a gardener (possession)
  3. the type of shed typically used by gardeners (description)

Additionally:

Rephrasing is the only way to disambiguate but it is often a clumsy alternative and many prefer to leave the ambiguity standing and rely on the context to make it clear which meaning of the genitive is intended.

Another function of the genitive is described as objective insofar as it refers to the object of a verb.  For example:
    the woman's imprisonment
probably refers to the fact that the woman is the object and was imprisoned but it needn't because it can be a subject genitive as in:
    the woman's imprisonment of the children
in which the woman is the subject and did the imprisoning.  From that we can then abstract a genitive:
    the children's imprisonment by the woman.
But, in order to disambiguate, we have to select a different form of the genitive and use the of-phrase, periphrastic structure instead of the 's inflexion.  Then we can arrive at a distinction between:
    the imprisonment of the woman
and
    the woman's imprisonment
which is less ambiguous, although still not wholly unambiguous.

Another example is:
    the man's investigation
which could mean:

  1. the investigation into the man
    or
  2. the investigation done by the man

If a. is intended then
    the investigation of the man
is preferred (the man was investigated, not the man did the investigation).
If b. is the preferred sense then
    the man's investigation
will be preferred, but ambiguity remains.
The rule of thumb is to reserve the of formulation for objective genitives and keep with the 's formulation for humans in subjective genitive expressions whenever there is a need to avoid ambiguity.

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no

Negation

What do you understand by the following negative statements?
    He didn't speak to the girl in the red dress at the party.
    She didn't meet the man who bought the house on Thursday.

Both sentences are ambiguous and mean either:

  1. He didn't speak to the girl in the red dress
    or
    He spoke to the girl in the red dress but not at the party
  2. She didn't meet the man who bought the house
    or
    She met the man who bought the house but not on Thursday
    (In this case, too, incidentally, we do not know whether the Thursday applies to when she didn't meet the man or whether the man bought the house on Thursday.)

We can disambiguate these to some extent when speaking by stressing the element we want to negate:
    He didn't speak to the girl in the red dress at the PARTY.
    She didn't meet the man who bought the house on
THURSDAY.
    He didn't speak to the girl in the red
DRESS at the party.
    She didn't meet the man who bought the
HOUSE on Thursday.
Or, as we saw above we can subtly alter where the tonic stress falls.
So, in the first two, we have party and Thursday as the nucleus with no tail and in the second we move the nuclear stress to dress and house and have a falling tone on the tails, at the party and on Thursday.

In written language, no such resources are available so we have to alter the ordering of the elements to make meaning clearer.
For example:
    At the party, he didn't speak to the girl in the red dress.
    On Thursday, she didn't meet the man who bought the house.

Even then, some ambiguity might remain so to be 100% clear, we need to rephrase entirely with something like:
    He didn't speak to the girl in the red dress until after the party.
    She didn't meet the man who bought the house until the following Friday.

As you see, the tendency in English to apply negation to phrases rather than words can lead to a considerable amount of ambiguity.
A general, if sloppy, rule is:

If the negation is ambiguous, hearers will usually assume that it is the final part of the sentence that is being negated.

So for example:
    He didn't drive
means he travelled in a different way
    He didn't drive my car
implies he drove his own or someone else's car
and
    He didn't drive my car carefully
will normally be understood to mean:
    He drove my car carelessly
rather than
    He didn't drive my car
In other words, to re-state the rule slightly differently

If there is a danger of some ambiguity, the scope of negation is confined to the final element of a negative utterance.

Occasionally, especially in writing where the use of emphasis, tone units and special sentence stress is less available, some negative statements can be ambiguous and must be rephrased to make the scope of negation clear.

She didn't praise any of the children could mean She praised no children at all or She praised only carefully selected children
They didn't drink half the beer Half the beer remains More than half the beer remains
This doesn't affect a few of you A few of you are unaffected All of you are affected
He wasn't promoted due to his working style There was another reason he was promoted His working style was the reason he wasn't promoted
I can't understand all of what he says I understand nothing he says I understand some of what he says

In spoken language, the senses can be disambiguated by stressing the determiners any and a few, stressing the pre-determiners half (of) and all (of), stressing the preposition due to and by placing a rising intonation contour on his working style.
In written English, that form of disambiguation is not available so careful writers will rephrase to avoid the possible confusion.

English is unusual in forming what is called transferred negation (for much more, see the guide to negation, linked below).  This means, for example, that we prefer:
    I don't think he's coming
over
    I think he's not coming
even though the second of these is more logical.
There is, however, a danger of some ambiguity when negation is transferred (or understood to be transferred). So, for example:
    John doesn't think his sister is happy
can be interpreted two ways:

  1. John believes his sister is unhappy
    or
  2. John does not think his sister is happy, he knows she is.

The second interpretation is rare and will be signalled as such, either by the insertion of an additional clause as above or by heavy emphasis being placed on the main verb.

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theme

Theme and rheme

Careless handling of theme and rheme often results in ambiguity or, at least, some confusion.
For example, if we take the two alternative forms:

  1. She wanted to see her sister so she took the train to London
  2. She took the train to London because she wanted to see her sister

we need to understand that they are not synonymous and simply randomly selected alternative forms.

In sentence 1. the Theme is
    She wanted to see her sister
and the rheme is she took a train to London
In sentence 2. the theme is
    She took the train to London
and the rheme is she wanted to see here sister
The theme is the jumping off point and the rheme acts to complete the thought.

Now, because rhemes form the following themes in coherent English, naturally, the first sentence would be followed by a second saying something about London (the rheme of the first sentence), such as:
    While she was there, she took the opportunity to visit the British Museum
and the second sentence would be more naturally followed by something about the sister such as:
    She was delighted to see her
If we follow the first sentence with something more appropriate to the second we get:
    She wanted to see her sister so she took the train to London.  She was delighted to see her.
in which we are left in a state of ambiguity regarding who was delighted to see whom because we have been ambushed by the incoherent use of theme-rheme structure and expected to read or hear something about London.

Moral: rhemes are used as themes in following sentences to avoid ambiguity.

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case

Case pronouns 

Case is not evident in English except in the realm of pronouns where it is critical to understand what did what to whom or whose item was whose.

Consider these two sentences:

  1. She likes you more than I
  2. She likes you more than me

In sentence 1., the meaning is that
    She likes you more than I like you
but in sentence 2. it is
    She likes you more than she likes me
It is only by insisting on the use of the correct case for the pronoun that the ambiguity can be avoided so the informal
    She likes you more than me
could carry either meaning.

The ambiguity is very common because in informal speech, the accusative (object) case of the pronoun is conventionally used so, e.g.:
    He likes spicy food more than me
would normally be interpreted as:
    He is more fond of spicy food than I am
although, because the accusative pronoun, me, has been used, it really means:
    He is more fond of curry than he is fond of me
The only way to disambiguate is to use rather formal and correct language and say:
    He likes spicy food more than I
to mean we are comparing tastes, and reserve
    He likes spicy food more than me
to mean we are comparing taste for food with liking for a person.

An additional issue with pronoun forms concerns the fact that the English system is defective, not always distinguishing case, so, for example, the pronoun you serves for all cases in English.  It is simply impossible in the following to decide what the sentence means:
    He likes Mary more than you
could mean:
    He likes Mary more than you like Mary
or
    He likes Mary more than he likes you

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2

Adjuncts, conjuncts and disjuncts

There is on this site a long guide to adverbials, linked below.  For now, we just need to know that adjuncts modify adjective, adverb and verb phrases, conjuncts link whole clauses and sentences together (which is why they are sometimes called linking adverbials) and disjuncts modify the whole of clauses, not just the verb phrase (which is why they are sometimes called sentence adverbials).

Conjunct problems

If the adverb is not separated by commas or by pausing between separate tone units from the rest of the clause, then some ambiguity arises.  For example:
    Her husband was displeased and she ended up similarly unhappy
means that we are comparing her unhappiness with her husband's displeasure so the adverb is only modifying the adjective, which is commonly what adverbs do.
However,
    Her husband became displeased and she ended up, similarly, unhappy
betokens that we are comparing her ending up unhappy with her husband's becoming displeased and the adverb is functioning as a conjunct linking the whole second clause to the first.

Fronting the adverbs removes the danger of ambiguity so the adverb in:
    Her husband became displeased.  Similarly, she ended up unhappy
is  only interpretable as a conjunct.

Disjunct problems

One of the examples in the opening tables was:
    Being honest, he was seen as rude

Which is interpretable in two ways:

  1. My honest opinion is he was seen as rude
    or
  2. Because he was honest he was seen as rude

There, it was listed under syntactical ambiguity but it is also a semantic problem because the hearer does not know who is being referred to as honest so the issue considered here.
If the speaker wishes to make it clear that he or she is trying to be honest then the phrase Being honest attaches to all that follows.  It is a style disjunct because the speaker is signalling how the hearer should understand what is said.
We can rephrase to remove the ambiguity, of course, as:
    Because he was being honest he was seen as rude
or
    If I may speak honestly, he was seen as rude

Other disjuncts can also be interpreted as adjuncts unless the phrasing in speech is carefully produced and punctuation is used successfully.  Even then, however, ambiguity can remain without rephrasing the thought.  For example:

and so on.
All three examples have the disjunct separated off by commas at the beginning of the sentence as is conventional so they should be understood as disjuncts referring only to the speaker's style.  They will, however, especially in rapid speech, often be misinterpreted as reference to the subject and verb phrase so rephrasing is often the only solution.
Prepositional phrases, despite the polysemous nature of prepositions themselves, instead of non-finite verb forms often help so we could get, e.g.:
    In fairness, Mary treated everyone equally
    On balance, the man was quite objective
    Between you and me, the accountant has told me the truth

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limit

Limiters

These adverbials (which are almost always adverbs) limit the range of the verb in some way.  The usual list includes:
    She only bought a shirt
    They even lied about the results
    They just left it where they found it
    I merely asked
    She nearly succeeded
    I simply want an answer

They need careful handling in terms of word ordering to avoid ambiguity.  Some can act outside the adverb role and even when they are adverbs, placement is important.
For example:
    Only he came to the meeting (nobody else came [determiner])
    He only came to the meeting (and did not speak [adverb])
    He came only to the meeting (and to nothing else [adverb])
    He came to the only meeting (and there was only one meeting [adjective])
all mean something slightly different as do:
    She just washed the shirt
    She washed just the shirt

because the first implies that she did nothing else to the shirt and the second that she washed nothing except the shirt.
Other examples of what happens when we move the limiters are:
    They lied even about the results
    They left it just where they found it
(in which the meaning of just changes from only to exactly)
    I want simply an answer

The rule of thumb to avoid ambiguity is to place the limiter immediately before the item it modifies.

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talk

Pragmatic ambiguity

All speakers of all languages, everywhere, occasionally misunderstand each other.  Most will have some kind of idiom akin to getting the wrong end of the stick although whatever it is is unlikely to be about sticks.
There is a guide on this site, linked below, to pragmatics which covers this area in a little more detail.  Here, we will deal with two related concepts.

punch

Illocutionary force

This is to do with what it is the speaker's intention to communicate, independent of the form of the language used to realise the function.
For example, a question such as:
    Would you like to try that again?
may, in fact, be an imperative meaning:
    That was not good enough.  Try again
but, if the hearer and speaker are at odds with what it means the preferred response of:
    OK, sorry.  I'll have another go
might be replaced by the dispreferred
    No, not really.
It may also be a threat along the lines of:
    If you try that again, I will retaliate
but the hearer may not comprehend the intention behind the question and ambiguity and misunderstanding will occur.  There is more on this in the guide to pragmatics, of course.

cooperate

The cooperative principle

We owe this concept to Grice (who gets much more discussion in the guide to pragmatics) who was concerned to elucidate how people figure out what the illocutionary force is that lies behind the language they hear or read.
He settled on four maxims, the breaking of any of which will signal some unexpected intention.  The four are:

  1. Quality: Don't say what you believe to be false.
    Breaking this maxim can result in some ambiguity because saying, e.g.:
        I don't see the argument
    may be ambiguous if the speaker intends to say
        I disagree
    (i.e., does understand the argument but doesn't like it)
    but the hearer understands
        Please explain again
    and goes on to do so, reiterating the argument to the exasperation of the hearer.
  2. Quantity: Be informative enough and don't over-inform.
    Breaking this maxim can also result in ambiguity because if a speaker says, e.g.:
        There's someone at the door
    the hearer (who has heard nothing) may take that to be simple information on which there is no need to act but the speaker may intend
        I know you heard the doorbell and I'd like you to answer it
    and is deliberately over-informing to make the point.
  3. Relation: Be relevant.
    If, in a conversation about getting the car repaired one speaker suddenly intrudes with, e.g.:
        By the way, do you have Anne's phone number?
    the hearer may suffer from a good deal of ambiguity until the speaker makes it clear that Anne is a car mechanic.
  4. Manner: Avoid obscurity.  Avoid ambiguity.  Be brief.  Be orderly.
    Any of the many ways in which the language can exhibit ambiguity discussed in this guide, whether lexical, syntactical or semantic, can lead to breaking this maxim.
    If, for example, a speaker says:
        I expected Mary would meet me before I got to the airport
    the hearer may perceive ambiguity in terms of whether the meeting or the expecting happened before the speaker arrived at the airport and wonder if the speaker is being intentionally or accidentally ambiguous.  It may take a little while to sort this out.

For more, see the guide.

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Summary

Here's a diagram that considers the main areas only:

summary



Related guides
polysemy and homonymy for some discussion of the fuzziness of these concepts with more examples
time, tense and aspect for more on the mismatch between tense form and the time it refers to
adjectives for more about post-positioning of adjectives and much else
lexicogrammar for some more about how attention to meaning affects syntax
Chomsky for the guide considering his views on ambiguity and much more
clause constituents for the guide to a major area
cleft sentences for the guide to how particular clause constituents may be marked by alterations to the grammar
negation for much more about assertive and non-assertive forms and transferred negation 
adverbials for much more about adjuncts and disjuncts (and other things)
pragmatics for the guide which contains consideration of the cooperative principle and more


Reference:
Wells, JC, 2006, English Intonation: An Introduction, Cambridge: Cambridge University Press