Having expelled quality from the field of extension, [idealists] do not know how to account for it when it reappears in thought. - Étienne Gilson

The scientific sterility of the Middle Ages has to be condemned for the same reasons which make it necessary today to condemn the philosophic sterility of scientism.

The mathematician always proceeds from thought to being or things. Consequently, critical idealism was born the day Descartes decided that the mathematical method must henceforth be the method for metaphysics.

Indeed, all idealism derives from Descartes, or from Kant, or from both together, and whatever other distinguishing features a system may have, it is idealist to the extent that, either in itself, or as far as we are concerned, it makes knowing the condition of being.