1.3.2. Some complications
Probably no one ever believed that the operation of language was as simple as this picture suggests, but it or something like it was, until recent decades, the working model most logicians used for thinking about the function of language. Around the middle of the 20th century, philosophers became interested in a number of features of language that suggest this picture is inadequate; and these features have been incorporated into a number of richer models of language. The norms of deductive logic that we will study do not rest on the richer structure of these new models, so we will not consider them in detail. But some of the further features of language that they attempt to capture are intertwined with those we will study, so we need to take some time now to disentangle ourselves from a few of these features once and for all and to lay the groundwork for disentangling ourselves from others at later points in the course.
The complicating phenomena that we need to consider have come to be studied under the rubric of pragmatics. This term was originally introduced (by Charles Morris) as an alternative to semantics in order to distinguish issues concerning the relation between language and its users from the issues concerning the relation between language and what is spoken of. Its meaning is now less closely tied to this definition than to commonly agreed examples of pragmatic phenomena, including the following.
1) Sentences are not always used to express propositions. When a sentence is used to express a proposition, the question of its truth value is a significant one. But not all sentences have truth values or raise questions of truth value. And even when a sentence does have a truth value, its truth value may not be its most important feature. There are many ways of using sentences, many speech acts, besides assertion; and the way a sentence is used is an aspect of its meaning that for which the term force is often used.
2) The information we derive from the use of sentences is not limited to what follows from accommodating them as true. Assertions can be expected to have properties other than truth, and the assumption that an assertion has these further properties can be the basis for deriving information from it. This produces the phenomena of implicature, in which a sentence suggests more than it says, and false implicatures can make true sentences misleading.
3) Sentences may have truth values in some possible worlds and not in others. There can be preconditions for a sentence to have a truth value. Such conditions are known as a (semantic) presupposition of the sentence, which can be said to presuppose that they are met.
4) The proposition expressed by a sentence (and thus its truth value) may vary with the context in which it is used. For example, there is no way to judge the truth value of a sentence like I put that here yesterday when it is taken out of context. This dependence on context is due to various phenomena known collectively as indexicality or deixis (some of which concern the role of the words I, that, here, and yesterday). The term character has been used for the way the proposition expressed depends on the context.
5) Even with regard to a given context, a sentence may not have a definite truth value. The meaning of vague terms like small and hot will vary with the context; and even in a given context there will be no sharp delineation of the cases where they apply truly. We can continue to speak of the character of a sentence containing such terms but only if we allow the proposition expressed to be depend on factors that are not fully determined in actual contexts of use.
It will be easy to disentangle ourselves from but others will require more detailed consideration. The force, implicatures, presuppositions, and character of a sentence are parts of its meaning in the fullest sense, and will consider each at least briefly to set our focus on the proposition expressed in the proper context.