 Psychologically we are limited to just the very first few numbers if we want to conceive of them properly, with higher numbers our short term memory is not enough to think of them all together, but still as identical to themselves and different from all others.Hence, Husserl says, we have to move on to the analysis of symbolically conceived numbers, which are effectively those that are used in mathematics.The book is a product of Husserl's years of study with Weierstrass (in Berlin) and his student Leo Königsberger (in Vienna) on the mathematical side and his studies with Brentano (in Vienna) and Stumpf (in Halle) on the psychological/philosophical side.