phi_270_text_1_3

We have been using the term imply so that a sentence implies anything whose content is included in the proposition it expresses. Thus we can say that the sentence My class was taught this morning implies A class was taught. The philosopher H. Paul Grice employed the term implicates to capture a different idea that is sometimes expressed by the ordinary use of the term implies. It is not uncommon for information to be suggested by a sentence even though it is not entailed and thus is not part of what the sentence literally says. For example, my assertion of the sentence My class was taught this morning would, in most contexts, suggest that I did not teach the class myself. However, this is not part of what I said since my statement would be perfectly true if I taught the class, so My class was taught this morning implicates I did not teach my class this morning but does not imply it.

The contrasting vocabulary suggest and say was used in passing in the previous paragraph, and it is a convenient way of expressing the difference between implications and implicatures. However, the term suggest could be misleading. In particular, it is not intended in this use of it to convey the idea of subjective association. What a sentence implicates can be as much the product of rules of language as what it implies; but the rules leading to implicature are not (or are not only) rules assigning truth conditions.

To see what they might be, let us consider an extension of our simple model of language use that accommodates implicature; in its outlines, it is due to Grice. To account for implicature, we extend the scope of accommodation to include not only the truth of assertions but also other features assertions ought to have. The maxim Speak the truth! is no doubt the key rule governing assertions, but other maxims, such as Be informative! and Be relevant!, also play a role. Someone who assumed I was obeying all maxims of this sort when I said, My class was taught this morning, might reason as follows:

Although Helman’s assertion My class was taught this morning would have been perfectly true if he had taught his class, it would have been a strange thing to say in that case because the proposition expressed by I taught my class this morning would have contained more information and information that would have been equally relevant. So I can best accommodate his use of language if I assume he did not teach the class.

Let us adopt some further current terminology and say that an assertion is appropriate when it is in accord with all maxims governing language use and that it is otherwise inappropriate. An assertion could be inappropriate even though true, and we usually accommodate our beliefs about the world to the assumption that the assertions others make are not only true but appropriate for the context in which they are made.

These ideas can be used to state contrasting definitions for implication and implicature. First let’s define implication in a way that will make the comparison easier:

φ implies ψ if and only if φ cannot be true (in a given context) when ψ is false (in that context).

To define implicature, we follow the same pattern using the concept of appropriateness instead of truth.

φ implicates ψ (in a given context) if and only if φ cannot be appropriate (in that context) when ψ is false.

That is, while implications are conditions necessary for truth, implicatures are conditions necessary for appropriateness. (Notice that this way of summarizing the definitions follows the grammatical pattern of implication and uses the term implicature for the things a sentence implicates as well as for the relation between a sentence and these things.)

One aspect of the relation between the two ideas depends on whether we regard truth itself as one of the requirements of appropriateness. We will do so since this makes the relation between these ideas easier to describe, but there is no consensus about using the terms in this way, and many would use implicature more narrowly to cover only those conditions necessary for appropriateness that are not necessary for truth.

Both definitions above refer to the context in which sentences are used. We have ignored this so far in the case of implication though the phenomenon of indexicality means that such a reference is often required. In any case, it is crucial for appropriateness: while the contextual dependence of truth values is tied to specific vocabulary, appropriateness in the wider sense is always dependent on the specific context in which a sentence is used. In the example used above, if it was well known that I had made a bet that I could avoid using the word I for the next 24 hours, no one would take its absence to be inappropriate when I had taught the class.

However, while appropriateness as a whole depends on the context, there are specific conditions attached to particular words that can lead to implicatures in every context. Consider, for example, this bit of dialogue:

Q: Was the movie any good?

A: Yes. Even John was laughing.

The assertion Even John was laughing has a number of implicatures that depend on the conversational setting (e.g., that John was at the movie and, perhaps, that it was a comedy), but it also has one that derives from presence of the word even. This implicature is easier to recognize than to state, but it comes to something like the claim that it is hard to make John laugh.

Implicature is a form of non-deductive inference that we will not study in its own right, but we will not be able to ignore it because it is often difficult to distinguish from implication. This is especially true for implicatures that attach to particular words because they have the same sort of independence of context that holds for the sorts of implications we will study.

One test that can be used to distinguish implicatures from implications is to ask a yes-no question. When asked Was even X laughing? about someone X who had laughed at the movie but who laughed easily, we would not answer with a simple No but rather say something like, Yes, but he’ll laugh at anything. Such yes-but answers indicate that the sentence we were asked about is true but inappropriate. Other qualified affirmative answers can play a similar role, and we will refer to them also as yes-but answers. To simply answer Yes in cases where a sentence is true but has a false implicature could mislead our audience into thinking that the sentence is entirely appropriate and thus that the implicature is true. Indeed, a true sentence with a false implicature could be described as true but misleading. Yes-but answers acknowledge the truth of such a sentence while correcting its misleading suggestions. (There are further tests that can be used to distinguish implicatures and implications, and we will consider some others in 4.1.2.)