[<nowiki/>Abraham Gotthelf Kästner is] the best mathematician among poets and the best poet among mathematicians - Carl Friedrich Gauss

I scarcely believe that in psychology data are present which can be mathematically evaluated. But one cannot know this with certainty, without having made the experiment. God alone is in possession of the mathematical bases of psychic phenomena.

We must admit with humility that, while number is purely a product of our minds, space has a reality outside our minds, so that we cannot completely prescribe its properties a priori.

But in our opinion truths of this kind should be drawn from notions rather than from notations.