At first sight, there does not seem to be much of a problem with expressing the idea of possibility in English: it is a seemingly single idea with numerous linguistic realizations to choose from. The problem, however, is that these realizations are not all interchangeable: different situations require different choices to be made.

Further investigation suggests that the different ways of indicating possibility express slightly different meanings. In other words, the idea of “possibility” actually covers a range of sub-meanings, rather like various other common grammar terms analysed within this blog, such as “necessity”, “existence”, “importance” and “conditional”. The result is that, in order to make the right linguistic choice in the expression of possibility, one must know and understand its various sub-meanings.

In this post I wish to explore these sub-meanings, along with the typical ways of expressing them. The outcome, I hope, will be a fairly complete overview of how and why the expression of possibility can vary in English. The first sections below deal with meanings and uses of the words possible and possibility, while the last examines some of their synonyms.

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USES OF “POSSIBLE”

The fundamental meaning of the adjective possible is “able to happen” or “able to exist”. Various sub-meanings are observable in particular sentences. Consider these:

(a) Time travel is possible.

(b) Currency exchange is possible here.

(c) Snow is possible today.

Sentence (a) associates something (time travel) with the general ability to happen or exist, rather than ability in a particular place at a particular time: the statement is of absolute possibility.

In (b), possible expresses ability of something (currency exchange) to happen in a particular situation, such as a shop. This leads to the additional suggestion of availability or usability.

Sentence (c) is also about a particular ability to happen or exist, but the happening or existence cannot be observed by the speaker (in this case because it is in the future). As a consequence, the additional idea of 50% probability is involved. This use of possible and its related adverb possibly is common in predictions and opinions (see 96. Making Statements More Uncertain 2, 107. The Language of Opinions, 121. Sentence-Spanning Adverbs

3 and 147. Types of Future Meaning

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Beyond these simple uses, possible has some more complex ones involving particular following words. One common type of following wording is a to verb e.g.:

(d) It is possible to travel in time.

Placing possible to after it + BE in this way seems to be standard. Starting with the possible idea, as in the following, is not recommended:

(e) ?Time travel is possible to achieve.

For the probable reason why a starting it is preferred, see 103. Representing a Later Statement with “it”.

Possible to expresses absolute possibility in (d), but this kind of sentence will often express one of the other basic meanings instead. Before a speech verb such as …to define or …to classify it further indicates that the writer’s own opinion is being given.

Quite often, possible and a to verb are separated by for and a subject noun. Again this can create extra meaning. Compare the following with (d):

(f) It is possible for most birds to fly.

(g) It is possible for graduates to undertake further study.

Sentence (f) names an absolute possibility (to fly) that is shown by for to apply only to some creatures. The sub-meaning might be described as capability, easily paraphrasable with the words have the capability of -ing. Sentence (g) too would, if understood as a statement of general rather than particular ability to happen, illustrate the sub-meaning of capability.

On the other hand, if (g) is understood as a statement by a university about its graduate entry policy, so that it expresses particular rather than general ability to happen (with the added idea of availability), possible will also carry the idea of opportunity or even permission. Unlike (f), it could be paraphrased with have the opportunity to or are allowed to.

Both capability and opportunity/permission imply desirability of the possible thing. I see the difference between them to lie in the source of the possibility. Capability comes from within – the person or thing possessing it is also its source. For example, birds’ capability of flight comes from something that is part of them – their wings. Opportunity and permission, on the other hand, are possibility sourced from outside – the source is not in the person or thing possessing the possibility. For example, the opportunity of graduates to undertake further study comes from other people’s rules. Possessing a degree may be necessary but not sufficient.

Sometimes possible is followed by for without a subsequent to verb. The to-verb meaning must then usually be expressed by the subject of the sentence, as in these rephrasings of (f) and (g):

(h) Flight is possible for most birds.

(i) Further study is possible for graduates.

The subject nouns here are both of the “action” kind (see 131. Uses of “Action” Nouns) – probably common in such sentences. The sub-meanings of possible are the same as those in (e) and (f).

Another typical word after possible is that (see 153. Conjunction Uses of “that”). Again, there is usually a starting it:

(j) It is possible that life exists on other planets.

This kind of sentence seems most likely to express the 50% probability meaning of possible. Indeed, sentences that express this meaning with …is possible, such as (c) above, seem to be particularly paraphrasable with possible that (It is possible that it will snow today).

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USES OF “POSSIBILITY”

Like possible, the noun possibility is usable either by itself or with typical following wording. By itself it is often used within the phrase is a possibility:

(k) Time travel (or currency exchange or snow) is a possibility.

As the choice of subjects shows, this use can equally express absolute possibility, availability and 50% probability. Availability sometimes has the idea of “option” or “alternative” added to it. This happens where the existence of alternatives is obvious, as for example in the following:

(l) One possibility is the dollar.

Here, one implies the existence of others (see 263. Uses of “One” and “Ones”). For another approach, see 266. Indicating Alternatives,

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The typical following words of possibility are of and that (rarely to – see 78. Infinitive versus Preposition after Nouns). With these, possibility can occupy any of the normal noun positions in a sentence, but is especially common after There is:

(m) There is a possibility of snow/time travel.

(n) There is a possibility that it will snow.

As these suggest, adding of can express either absolute possibility or 50% probability, while adding that expresses only the latter. Sentence (n) is very similar to (j) – indeed, it could be paraphrased with a starting It is possible…. More on the similarity of It and There sentences is in 161. Special Uses of “There” Sentences.

The sub-meanings of capability and opportunity or permission are less common with possibility than possible. This is because the verb HAVE, the natural choice for linking these meanings with their possessor, typically does so with other nouns than possibility as its object: (cap)ability or chance or opportunity or permission. Thus, paraphrasing sentence (f) with have requires an object like the ability to fly, not *the possibility of flying; and (g) would probably say have the opportunity to undertake…. Note that occasion is not a synonym of opportunity (see 236. Tricky Word Contrasts 9,

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Perhaps the most acceptable use of possibility after HAVE is to express 50% probability, e.g.:

(o) The hypothesis has a possibility of being correct.

However, even here chance seems equally if not more natural.

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OTHER POSSIBILITY WORDS

1. Synonyms of “Possible” and “Possibility”

Many adjectives express the idea of possibility through the suffix -able (or -ible). For example, acceptable means that accepting is possible, divisible that dividing is. Usually, the part without the suffix corresponds to a passive verb. For more examples, see 27. How to Avoid Passive Verbs and 106. Word-Like Suffixes.

Although it is normally only the suffix that expresses possibility in such words, there are a few instances where the whole word is a synonym of possible. The following adjectives seem at least sometimes able to express one or other of its meanings.

ALTERNATIVE: available, usable, alternative

50% PROBABLE: feasible, potential

ABSOLUTELY POSSIBLE: achievable, conceivable, feasible, imaginable, real, viable

ABLE TO BE DONE BY SB/STH: achievable, viable

EXISTING AS AN OPPORTUNITY: achievable, available, open

ALLOWED: allowed, permitted

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On the other hand, possibility has at least the following noun synonyms:

ALTERNATIVE: an alternative, choice, option

50% PROBABILITY: a potential (+ for)

ABSOLUTE POSSIBILITY: a reality

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2. Modal Verbs

Can and/or may seem able to express all of the above meanings:

ALTERNATIVE: can, may (Cars can/may go left or right)

50% PROBABLE: may (It may snow)

ABSOLUTELY POSSIBLE: can (Mars can be reached)

ABLE TO BE DONE BY SB/STH: can (Most birds can fly)

EXISTING AS AN OPPORTUNITY: can (Travellers can learn languages)

ALLOWED: can, may (Only members can/may enter)

Despite these equivalences, it should not be thought that can and may only express possibility. For some other uses, see 237. Auxiliary Verbs in Professional Communication. As an example, can occasionally means “sometimes”, e.g. Cold can kill (see 95. Making Statements More Uncertain 1).

May is not the only modal verb that can express probability. Stronger or weaker strengths than that equating to “possible” are expressed by may well (around 70%), might (30%) and could (10%).

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3. Other Verbs

When “possibility” means “capability”, “opportunity” or “permission”, various other verbs are alternatives to can and may. BE ABLE TO and BE CAPABLE OF can directly replace capability-showing can.

Verbs like ALLOW, ENABLE, FACILITATE, LET and PERMIT need to be passive to have the holder of the possibility as their subject (Cars are permitted to…), but can also have it as their object by being in the active form (The law permits cars to…). For full details of their usage, see 65. Verbs that Mean “Must” or “Can”.

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4. “As if”

The 50% probability meaning of it is possible that is perhaps also implied by some uses of as if:

(p) It looks as if it is snowing.

We understand here that snow could actually be falling. In general, a statement after as if expresses possible truth when the verb tense is a natural one: present indicating present possibility, future (will snow) future possibility etc. Other verb forms deny the possibility: was snowing in (p) would clearly indicate no actual snow, was going to snow no imminent snow (see 191. Exotic Grammar Structures 3, # 3).