§33. Suppose, however, someone were to object: "It is not true that you must already be master of a language in order to understand an ostensive definition: all you need—of course!—is to know or guess what the person giving the explanation is pointing to. That is, whether for example to the shape of the object, or to its colour, or to its number, and so on."—And what does 'pointing to the shape', 'pointing to the colour' consist in? Point to a piece of paper.—And now point to its shape—now to its colour—now to its number (that sounds queer).—How did you do it?—You will say that you 'meant' a different thing each time you pointed. And if I ask how that is done, you will say you concentrated your attention on the colour, the shape, etc. But I ask again: how is that done?
Suppose someone points to a vase and says "Look at that marvellous blue—the shape isn't the point."—Or: "Look at the marvellous shape—the colour doesn't matter." Without doubt you will do something different when you act upon these two invitations. But do you always do the same thing when you direct your attention to the colour? Imagine various different cases. To indicate a few:
"Is this blue the same as the blue over there? Do you see any difference?"—
You are mixing paint and you say "It's hard to get the blue of this sky."
"It's turning fine, you can already see blue sky again."
"Look what different effects these two blues have."
"Do you see the blue book over there? Bring it here."
"This blue signal-light means...."
"What's this blue called?—Is it 'indigo'?"

You sometimes attend to the colour by putting your hand up to keep the outline from view; or by not looking at the outline of the thing; sometimes by staring at the object and trying to remember where you saw that colour before.
You attend to the shape, sometimes by tracing it, sometimes by screwing up your eyes so as not to see the colour clearly, and in many other ways. I want to say: This is the sort of thing that happens while one 'directs one's attention to this or that'. But it isn't these things by themselves that make us say someone is attending to the shape, the colour, and so on. Just as a move in chess doesn't consist simply in moving a piece in such-and-such a way on the board—nor yet in one's thoughts and feelings as one makes the move: but in [all] the circumstances that we call "playing a game of chess", "solving a chess problem", and so on.


  1. "...you concentrated your attention on the colour, the shape, etc. But I ask again: how is that done?" The interlocutor should reply "Why should I be able to tell you, in the public OL, how it is done?" The public OL is not designed to describe what is going on privately, as W. effectively points out throughout his remarks. Arguably what is going on is beyond the limits of language; it is certainly beyond what OL can directly communicate, since the private stuff is by definition only accessible by each one of us individually. Ostension will not work. 'Concentrating our attention...' is an attempt to refer, using public OL, to some private stuff. Pointing out that we cannot use this OL to describe the stuff properly, does not demonstrate that nothing is being pointed at.