抄録
This paper concerns so called ‘concept formation thesis' that we can find in Wittgenstein's philosophy of mathematics. I will deal with this topic by focusing on his view of the relation between a problem and its solution in mathematics. In his ‘middle' period, he had the view that some problems (or conjectures) expressed by the sentences involving quantification over infinite domains are senseless. This is very important because it suggests that the problem-solution relation is such that the solution gives the grammar to the problem. In a special sort of language activity, ‘riddle', words in the question also receives some new meanings from the answer. I will compare mathematics with riddle, which enables us to see the change of perspective that determines similarity and dissimilarity.
