§28. Now one can ostensively define a proper name, the name of a colour, the name of a material, a numeral, the name of a point of the compass and so on. The definition of the number two, "That is called 'two'"—pointing to two nuts—is perfectly exact.—But how can two be defined like that? The person one gives the definition to doesn't know what one wants to call "two"; he will suppose that "two" is the name given to this group of nuts!—He may suppose this; but perhaps he does not. He might make the opposite mistake; when I want to assign a name to this group of nuts, he might understand it as a numeral. And he might equally well take the name of a person, of which I give an ostensive definition, as that of a colour, of a race, or even of a point of the compass. That is to say: an ostensive definition can be variously interpreted in every case.

 

ELUCIDATION

  1. W. offers a kind of underdetermination, familiar also in the work of Quine (with rabbit, rabbit part, rabbit time slice, and indeterminacy of translation).
  2. I have here interpreted the first two sentences as being the interlocutor, suggesting that we can define 'two' precisely, exactly, beyond question, capturing its essence, teaching it unquestionably to someone else,  by pointing at the nuts and saying the right thing. This is going, supposedly, to set up the indissoluble link between the word, the state of affairs in the world, and, presumably, the idea of twoness in our mind.
  3. The first two sentences could alternatively be interpreted as being in W.'s voice, in which case "is perfectly exact" would mean that this is exactly (correctly) what 'ostensive definition' means, in ordinary language - warts and all. He is then going to show that it is incomplete, that it is fallible; but that is nonetheless exactly how 'two' is ostensively defined.
  4. Doubtless there is a procedure of trial and error, of varying context, which makes different people's uses converge. Perhaps without an infinite number of different contexts, we can never establish whether two people's uses might eventually diverge; whether, roughly, they mean the same by 'love'.
  5. Maybe there is a genetically inherited similarity between humans, so that they tend to get the same end of the stick, presented with the partial clues. They have a natural tendency to supposed that 'rabbit' refers to the complete furry creature, rather than just to the creature's legs, or the creature now...
  6. Ostensive defining of a word and ostensive teaching of a word do not seem to be clearly distinguished. The first gives the impression that it is not anthropocentric, the latter that it is. Probably he would simply deny that these two are clearly separable, because they are fuzzy, like all words.