You may say: Two can be defined ostensively only in this way: “This number is called ‘two’”, for || . For the word “number” shows here || here shows in what place in the language – in the grammar – we set || put || what place in our language – in our grammar – we assign to the word; but this means that the word “number” must be explained before that ostensive definition can be understood. – The word “number” in the definition does certainly || indeed indicate this place, the post to which we assign || which we assign to the word. And we can prevent misunderstandings in this way, by saying, “This colour is called so and so”, “This length is called so and so”, etc.. That is: misunderstandings are often avoided in this way. But can the word “colour”, then, or “length”, be understood only in this way? – Well, we'll || we shall have to explain them. – Explain them by of other words, that is || That is, explain them by means of other words! And what about the last explanation in this chain? (Don't say: “There isn't any ‘last’ explanation”; that || . This is exactly as though you were to say || said, “There isn't any last house in this street: you can always build another one further”.) || .”)
     Whether the word “number” in the ostensive definition of two is necessary || is necessary in the ostensive definition of “two” depends on || upon whether he understands this word differently from the way I wish him to || takes this word in a different sense from the one I wish || misunderstands my definition if I leave out the word. And that || this will depend on the circumstances under which the definition is given and on the person to whom I give it.
20
¤
     And how he “understands” the explanation appears in how || will appear in the way he makes use of the word explained.