Definition by ostension
As we saw in Chapter 1, the most obvious way to defi ne many words is, simply, by ostension, or by pointing out the objects which they denote. In spite of the apparent obviousness of this method, it is beset by difficulties. Firstly, as we saw in Chapter 1, verbs, adjectives and prepositions are not open to this definitional method, to name only the lexical categories most familiar from English: if you point at a black cat running along a wall, you are pointing at a cat, not at ‘black’, ‘running’ or ‘along’. Secondly, even in the case of objects, ostensive definition is extremely problematic. To illustrate this, imagine the following situation. You are in an optometrist’s shop in France, trying to buy a new pair of sunglasses. You speak a little French, but are confused by the fact that the shop assistant continually refers to something called a [VεR]. You ask what this word means, and in reply, the shop assistant taps several times with his index finger on the lens of the pair of sunglasses he is holding. This is a canonical instance of ostensive definition: the meaning of a word has been defined by indicating the object to which it refers. But exactly what part of the pair of glasses is being indicated? Is it the whole thing? In that case [VεR] must mean ‘glasses’. Or is it just the lens as distinct from the frame, in which case [VεR] will mean ‘lens’? If so, does it mean ‘glasses lens’ and ‘camera lens’ and ‘contact lens’, or only the fi rst? But perhaps [VεR] only refers to the particular type of tinted, nonreflective sunglasses lens which the shop assistant is holding: perhaps other lenses, with different shapes, compositions or functions, have different names. Or does [VεR] refer to neither the lens nor the frame proper, but simply to the front, most visible part of the glasses, the lenses and those parts of the frame which are in contact with the front of the face?
QUESTION Would it be possible to eliminate these uncertainties purely ostensively? If so, how? If not, why not?
None of these questions can, in fact, be settled by ostensive definition: every attempt to make the definition more precise ostensively would give rise to a new set of questions. Although it is an appealing idea that meanings can be defined simply by pointing at objects in the world, in practice this definitional method would seem to give rise to too many ambiguities to be viable.
The only way to overcome the problems of ostensive definition would seem to be to use language itself as the medium in which definitions can be phrased: only this way, apparently, can we get the level of definitional precision we need. There are several ways in which this can be done. We will discuss definition by synonymy, by context and typical exemplar, and by genus and differentia.
