Quote:
Could one define the word "red" by pointing to something that was not red? That would be as if one were to explain the word "modest" to someone whose English was weak, and one pointed to an arrogant man and said "That man is not modest". That it is ambiguous is no argument against such a method of definition. Any definition can be misunderstood.

But it might well be asked: are we still to call this "definition"?—For, of course, even if it has the same practical consequences, the same effect on the learner, it plays a different part in the calculus from what we ordinarily call "ostensive definition" of the word "red".

[...]

273. What am I to say about the word "red"?—that it means something 'confronting us all' and that everyone should have another word, besides this one, to mean his own sensation of red? Or is it like this: the word "red" means something known to everyone; and, in addition, for each person, it means something known only to him? (Or perhaps rather: it refers to something known only to him.)

Ludwig Wittgenstein Philosophical Investigations translated by GEM Anscombe, pp.14 and 95.

Ceci n'est pas un seing.