§187

Wittgenstein agrees with the interlocutor that it makes sense to say that, "I already knew that B should write 1002 after 1000 when I gave the order". Philosophical/conceptual confusion can arise if this is misconstrued, however.

To say that you meant for B to write '1002' after '1000' when you gave the order '+2' does not mean that you thought of the step when you gave the order.

The interlocutor says that, "if I had been asked what number he [B] should write after 1000 I would have replied '1002'". Wittgenstein says that he doesn't doubt this. Does this mean that meaning something means having certain dispositions?
--Philosophical problem: would it mean that you'd have to have had an infinity of dispositions? - If you were asked what number B should write after 5,016 is it clear that you'd have replied '5,018'? And 10,314 after 10,312 etc. etc.

Wittgenstein wants to get away from the confused idea that knowing something is an event that occurred simultaneously with giving the order (the interlocutor says 'I..knew, at the time when I gave the order...'). Wittgenstein has already made the point, in §150, that the grammar of the word 'know' is closely related to 'can' and 'is able to'.

When Wittgenstein says that it would be correct for A to say, "if I had then been asked what number he should write after 1000, I would have replied '1002'" he says so because he does not doubt that A has mastered basic mathematics - that A is able to add 2 to any number (not because A thought of this case at the time of giving the order).