82 Defining the meaning of words

semantics, as we shall see later, has exploited and developed the distinction between extension and intension in various ways. And some scholars have actually identified the sense of an expression with its intension. For reasons which become clearer later, I prefer to treat extension and intension as com­plementary aspects of denotation. Regardless of the view that one takes of the ontological status, or reality, of properties, it is convenient to be able to say that an expression denotes (extensionally) a class of entities and (intensionally) its defining property (i.e. the property which all members of the class share and by virtue of which they are members of the class in question). For example, it is convenient to be able to say that the word 'red' denotes, not only the class of red things, but also the property of redness. 'This, is intended to be a philo­sophically neutral way of talking: neutral with respect to the long-standing philosophical controversy between nominalists and realists and neutral with respect to the typically empiricist thesis of extensionality, which has been so influential in twentieth-century logic and philosophical semantics.

Finally, as far as this section is concerned, it must be empha­sized that nothing said here about sense and denotation is to be taken as implying that either the one or the other is fully deter­minate in the case of all, or even most, lexemes in the vocabul­aries of natural languages. On the contrary, the sense of most lexemes, and therefore of most lexically composite expressions, would seem to be somewhat fuzzy at the edges. Similarly, it is very often unclear whether a particular entity falls within the denotation of an expression or not. What then does it mean to say that someone knows the descriptive meaning of particular expressions in his or her native language? Indeed, how do we manage to communicate with one another, more or less success­fully, by means of language, if the descriptive meaning of most lexemes - their sense and denotation - is inherently fuzzy or indeterminate? This question will be taken up in section 3.4.

3.2 Basic and non-basic expressions 83

3.2 Basic and non-basic expressions

About half-a-century ago, Bertrand Russell drew a distinction, which has subsequently been much discussed by semanticists (in these or other terms), between what he called object-words and dictionary-words. The distinction itself was by no means original. But Russell expressed himself with characteristic lucid­ity, and the way in which he developed the underlying, initially appealing, principle makes his formulation of the distinction particularly interesting. Object-words, he tells us, "are defined logically as words having meaning in isolation, and psychologi­cally as words which have been learnt without its being neces­sary to have previously learnt any other words". Dictionary-words, in contrast, "are theoretically superfluous", since they are definable, and may be learned, in terms of the logically and psychologically more basic object-words (Russell, 1940: 62-3).

Leaving the non-basic dictionary words on one side for the moment, we may now ask how one comes to know the descrip­tive meaning of the allegedly basic object-words. Russell is quite clear on this point. Object-words are learned by demon­stration or, as philosophers say, ostension: that is, by showing the learner a sufficient number of entities that fall within the denotation, or extension, of each object-word. At its most expli­cit, ostensive definition - definition by ostension - would involve pointing at one or more entities denoted by the word in question and saying,

(1) That is a(n) X.

For example, pointing at one or more dogs, one might say,

(2) That is a dog.

Ostensive definition plays a prominent role, in theory if not always in practice, in the empiricist tradition, to which Russell belonged. So too does denotation. And Russell's definition of object-words makes it clear that their meaning, in contrast with that of dictionary words, is wholly a matter of denotation.

But the notion of ostensive definition has come in for a lot of criticism. In fact, it is readily shown to be indefensible in the