Now that we have separated sub-types of the phenomenon of multiple interpretability, we may reasonably ask how we tell which sub-type is appropriate in a given instance. The answer may be disappointing—there are tests and considerations but no firm answers and probably a lot will depend on what the ‘best theories’ in linguistics etc. end up looking like. Nevertheless, we can make some progress. The canonical source for these tests is Zwicky and Sadock’s ‘Ambiguity Tests and How to Fail Them’ (1975).
These tests generally depend on the presence or lack of interpretations and on judgments regarding the ridiculousness of interpretation (the absurdity of the meaning is known as zeugma—though it should probably be known as syllepsis). These judgments can be difficult to make especially in tricky philosophical cases, so expect that the tests may be of less help than we might hope for at first.

4.1 Conjunction Reduction

A standard test for ambiguity is to take two sentences that contain the purportedly ambiguous term and conjoin them by using the term only once in contexts where both meanings are encouraged. For example, ‘light’ is a predicate that can enjoy the same meaning as either ‘not dark’ or ‘not heavy’.
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[*]The colours are light.

[*]The feathers are light.

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The following, however, seems to be zeugmatic:
[list=39]
[*]?The colours and the feathers are light.

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The reduced sentence is zeugmatic for obvious reasons. This is evidence for ambiguity (or polysemy) in ‘light’. On the other hand, ‘exist’, which has been claimed to be ambiguous, seems not to display such zeugmatic effects:
[list=40]
[*]Toronto exists.

[*]Numbers exist.

[*]Triadic relations exist.

[*]Toronto and numbers and triadic relations exist.

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The test is limited in one way. If a term can be ambiguous but in a way so subtle that people miss it, then the zeugma might not be noticeable. Given that these tests try to draw on linguistic judgments to detect ambiguity, it’s not clear how to proceed when there is a case of disagreement over the presence of zeugma.
We can use the test in cases in which one wouldn’t necessarily expect zeugma, but merely lack of multiple interpretations. For example:
[list=44]
[*]Han and Chewbacca won superfluous hair removers.

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(44) doesn’t allow a reading on which Han won a hair remover that was superfluous and Chewbacca won a remover of superfluous hair. If multiple interpretations are impossible, there is evidence of ambiguity. This is to be expected since the point of conjunction reduction is to ‘freeze’ the syntactic structure and in ambiguous cases, the effect is achieved.
As mentioned above, conjunction reduction has been used to argue that collective-distributive ambiguities are due to an ambiguity in the subject phrase. Consider:
[list=45]
[*]John and Jane moved a piano.

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One might think that the readings are generated by an ambiguity in ‘and’: sometimes it acts as a sentential operator and sometimes as a term-forming operator that makes two names into a single term for predication. However, notice that there are some predicates that can only be (sensibly) interpreted collectively, such as ‘met’:
[list=46]
[*]John and Jane met for lunch.

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In this case, there is no sense to be made of ‘John met for lunch and Jane met for lunch’ and so the sentential conjunction reading is not available. Using conjunction reduction on (45) and (46) we get:
[list=47]
[*]John and Jane moved a piano and met for lunch.

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(47) has a reading on which ‘moved the piano’ is interpreted distributively (two liftings) and ‘met’ is read collectively. The felicity of the conjunction reduced (47) suggests that the ambiguity isn’t the result of an ambiguity in conjunction. (see McKay 2006). We can try to use the test in an extended manner on full sentences if we embed them under ‘says that’ or perhaps ‘believes that’: ‘John and Adam believe that Sarah bought a superfluous hair remover’ is infelicitous if the unconjoined sentences involve different interpretations of ‘felicitous hair remover’.
The test has certain weaknesses. In actual utterances, intonation can be used to indicate an assertion or an each question (‘Ben wanted to eat that?) conjoined with ‘Ben wanted to eat that’ yields an infelicity even if the demonstrative has the same value on both occasions—though we may try to fix things up by demanding that the test be run using common intonation (at least in spoken uses of the test!). On that note, the test will judge demonstrative and indexicals to be ambiguous since they are famously not generally conjunction reducible.

4.2 Ellipsis

Ellipsis tests work in a manner similar to conjunction reduction tests. For example:
[list=48]
[*]I saw his duck and swallow under the table and I saw hers too. (Zwicky and Sadock 1975)

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(48) can mean that I saw their birds under the table or that I saw their activities of ducking and swallowing but it can’t mean that I saw one’s birds and the other’s activities. Similar features hold for structural ambiguities:
[list=49]
[*]I’m happy that every man met two women and Jim is too.

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It isn’t possible to interpret (49) as having ‘every man’ with wide scope in one but narrow in the other. This suggests a real ambiguity in the scope of the two quantifiers. This test has led people some philosophers to surprising results. For example, Atlas (1989) argues that the acceptability of the following suggest that negation does not interact scopally with descriptions in the ways we have come to expect:
[list=50]
[*]John thinks that the King of France is not bald and Bob thinks so too.

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The purported availability of both readings suggests that sentences with negation and descriptions are sense-general rather than ambiguous, contradicting many standard assumptions about the computation of truth conditions. Alternatively, it may lead us to think that there weren’t as many readings as we initially thought there were (or that we have the wrong theory of descriptions).

4.3 Contradiction Tests

Another way to test for ambiguity is to test for lack of contradiction in sentences that look to be contradictory. For example, say someone argued that ‘aunt’ was ambiguous on account of not specifying maternal from paternal aunt. If that was the case, we would expect that we can access the two distinct senses of ‘aunt’ just as we did for ‘bank’. However, compare:
[list=51]
[*]That bank isn’t a bank.

[*]*She is an aunt but she isn’t an aunt.

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Both sentences are rather awkward but only one is doomed to contradictoriness. It’s pretty clear that we can read (51) as non-contradictory. This is good evidence that ‘aunt’ is unspecified with respect to which side of the family she comes from, but not ambiguous. The tests can be used for most of the other types of ambiguity (though not speech act ambiguity for obvious reasons):
[list=53]
[*]My superfluous hair remover is not a superfluous hair remover; (I need it!)

[*]The goose is ready to eat but it’s not ready to eat; (we need to cook it first.)

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(It helps to provide a paraphrase afterwards to bring out the distinct senses). The tests can be used to detect lexical, structural and thematic ambiguity.

4.4 Definitional Tests

Aristotle offers a test for ambiguity: try to construct a definition that encompasses both meanings and posit an ambiguity only if you fail. The notion of definition here has to be taken as a heavy-weight notion: ‘bank’ is ambiguous even though you can ‘define’ it as ‘financial institution or river side’. However, we can get a reasonable grip on what Aristotle had in mind. ‘Uncle’ is not ambiguous because it has a single definition that covers both: x is an uncle iff x is the brother of yand y has a child. ‘Pike’ doesn’t enjoy a single definition.
The test depends partly on how strict we are about what counts as a definition. As Fodor argues, there is a real paucity of satisfying definitions out there, suggesting that semantic atomism may be the norm in the lexicon. If atomism is right, there is good reason to think that nearly all the lexicon fails to submit to any interesting analyses in terms of necessary and sufficient conditions (see Fodor 1998).

4.5 More Spurious Tests

Kripke, in his famous attack on Donnellan, suggests a few tests for ambiguity that are more conceptual in nature. In particular, he makes the following intriguing suggestion:

اقتباس :

“Bank” is ambiguous; we would expect the ambiguity to be disambiguated by separate and unrelated words in some other languages. Why should the two separate senses be reproduced in languages unrelated to English? First, then, we can consult our linguistic intuitions, independently of any empirical investigation. Would we be surprised to find languages that used two separate words for the two alleged senses of a given word? If so, then, to that extent our linguistic intuitions are really intuitions of a unitary concept, rather than of a word that expresses two distinct and unrelated senses. Second, we can ask empirically whether languages are in fact found that contain distinct words expressing the allegedly distinct senses. If no such language is found, once again this is evidence that a unitary account of the word or phrase in question should be sought. (Kripke 1977: p. 268)

In other words, since lexical ambiguity should involve something like accidental homophony, one would expect that other languages would lexicalize these meanings differently. Thus, it would not surprise one to find out that the two meanings of ‘bat’ were expressed by two different words in other languages. It may well surprise one to find out that every action verb was lexicalized as two different verbs, one for a reading on which the action was done intentionally, one on which it wasn’t in some other language.
This test is not especially reliable, especially with respect to differentiating sense generality from ambiguity. It would not be surprising to find out that other languages lexicalize ‘uncle’ in two different words (in Croatian, there is no one word translation of ‘uncle’: ‘stric’ means brother of one’s father and ‘ujak’ means an uncle from the mother’s side). Nonetheless, there is no reason to think that ‘uncle’ is ambiguous in English. Why wouldn’t language users create words to designate the specific meanings that are left sense-general in a different language?

4.6 Problems for the Tests

4.6.1 Privative Opposites

Zwicky and Sadock (1975) argue that sometimes the two (or more) putative meanings of a word are related by overlapping except with respect to one or more features. The Random House Dictionary, for example, gives (amongst many others) the following two definitions for ‘dog’:

اقتباس :

2. any carnivore of the dog family Canidae, having prominent canine teeth and, in the wild state, a long and slender muzzle, a deep-chested muscular body, a bushy tail, and large, erect ears. Compare canid.
3. the male of such an animal.

Ignoring for now whether or not dictionaries manage to report analyticities (is having a bushy tail really an analytic necessary condition for being a dog?), it looks like sense (2) and (3) differ merely by specification of gender, and so if this makes for ambiguity, it may well be hard to test for. Similarly for verbs that allow a factive and non-factive reading such as ‘report’ where the factive reading entails the non-factive. If I say ‘the police reported that the criminal was apprehended but the police didn’t report that the criminal was apprehended’ there is at least one reading that is anomalous, but largely out of contradiction engendered by entailment rather than univocality: it takes subtle intuitions to train one’s ear to hear ambiguities when the meanings are largely overlapping. As mentioned above, Pietroski and Hornstein (2002) make a similar point regarding syntactic ambiguities. Noting that the two putative readings of ‘every man loves a woman’ are such that the wide scope ‘a woman’ reading entails the narrow, they ask whether or not we should be countenancing a structural ambiguity or chalking up the two ‘readings’ to confusion over the specific and general case. If these sorts of factors can interfere, we will indeed have to apply our tests gingerly.

4.6.2 The Inconsistency of Zeugma

A problem for the conjunction reduction test involves the context-sensitivity of zeugma. As noted by Lewandowska-Tomaszczyk (following Cruse 1986), the following two are different in terms of zeugma:
[list=55]
[*]?Judy’s dissertation is thought provoking and yellowed with age.

[*]Judy’s dissertation is still thought provoking although yellowed with age.

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Similarly, from the literature on generics:
[list=57]
[*]Bees thrive in warm environments and are swarming my porch.

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These cases looks like a problem for the conjunction reduction test, depending on how one thinks we should treat the ambiguity in generics. One might think that this provides evidence against ambiguity in bare plurals.