§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.

ELUCIDATION

  1. I doubt that anyone would suggest that the public events he summarises in the final paragraph ("tracing the shape" etc.) are the entire meaning of 'directing my attention at the colour of the sofa'. There is a further context - circumstances - which need to be present. But we might suggest that what is the entire meaning is the characteristic private experience (see §34 and §35). This is his target.
  2. Chess: A second appearance of the analogy, emphasising its pedagogical importance. The thoughts and feelings associated with X: "Moving a piece in chess", may be interesting to us - they are part of the form of life - but they are not definitive; they are not what a move in chess purely ("simply") consists in; they are not what X purely means. Similarly the physical moving of a piece of wood to a new  position is not what X purely means. There is no single thing that X means, or to which it refers.