 The existence of the natural numbers is given by the first act of intuitionism, that is by the perception of the movement of time and the falling apart of a life moment into two distinct things: what was, 1, and what is together with what was, 2, and from there to 3, 4, … In contrast to classical mathematics, in intuitionism all infinity is considered to be potential infinity. In particular this is the case for the infinity of the natural numbers. Therefore statements that quantify over this set have to be treated with caution. On the other hand, the principle of induction is fully acceptable from an intuitionistic point of view.