Consider this example: Suppose we had taught a man to use the words “green”, “red”, “blue” by pointing to patches of these colours. We had taught him to fetch us objects of a certain colour on being ordered, “Bring me something red!”, to sort out objects of various colours from a heap, and such like. Suppose we now shew him a heap of leaves, some of which are a slightly reddish brown, others a slightly greenish yellow, and give him the order, “Put the red leaves and the green leaves on separate heaps.” It is quite likely that he will upon this
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separate the greenish yellow leaves from the reddish brown ones. Now should we say that we had here used the words “red” and “green” in the same sense as in the previous cases, or did we use them in different but similar senses? What reasons would one give for adopting the latter view? One could point out that on being asked to paint a red patch, one should certainly not have painted a slightly reddish brown one, and therefore one might say “red” means something different in the two cases. But why shouldn't I say that it had one meaning only but was, of course, used according to the circumstances?