Because the one that says: I know that I am alive, he says that he knows the only thing. But if now he says: I know that I know that I am alive, now he already knows two. But to know these two is already in himself a third thing that he knows. And a fourth, and then a country house, and this way successively. But since it is possible neither to comprise an innumerable things addition, to say a thing innumerable times, we include it in the only concept and say that it is a question of an infinite number.

San Agustín de Hipona Vía Bulletin 210 (PDF) of the RSME.
Interesting appointment of San Agustín, in which the concept of mathematical induction is explained, between many other things. Much of the style of the famous person only I know that I do not know anything.