For want of sufficiently searching psychological investigations, Descartes was led to suppose that innumerable ideas, the evolution of which in the course of experience can be demonstrated, were direct or innate products of the thinking faculty.
As has been already pointed out, it is the great merit of Kant that he started afresh on the track indicated by Descartes, and steadily upheld the doctrine of the existence of elements of consciousness, which are neither sense-experiences nor any modifications of them.

We may demur to the expression that space and time are forms of sensory intuition; but it imperfectly represents the great fact that co-existence and succession are mental phenomena not given in the mere sense experience.[23] FOOTNOTES: [22] Remarques de Rene Descartes sur un certain placard imprime aux Pays Bas vers la fin de l'annee, 1647 .-- Descartes, _OEuvres_.Ed.

Cousin, x.p.

71.
[23] "Wir koennen uns keinen Gegenstand denken, ohne durch Kategorien; wir koennen keinen gedachten Gegenstand erkennen, ohne durch Anschauungen, die jenen Begriffen entsprechen.

Nun sind alle unsere Anschauungen sinnlich, und diese Erkenntniss, so fern der Gegenstand derselben gegeben ist, ist empirisch.