So he can make sure of what it means in this private way! || by having a private sensation in this private way of what it means! Making sure that you know what ‘seeing
red’ means is good only if you can make use of this knowledge in a future case. Now what if I see a colour again, can I say I knew made sure I knew what ‘red’ was || meant so now I shall know that I'll recognize it correctly? In what sense is having said the words ‘this is red’ before a guarantee that I now see the same colour when I say again I see red?