Universal reflections should have the first claim on our attention; but on the other hand the transition to the determinate is accomplished in a system of Physics which is the result of observations and experiences, and this is done entirely by means of the understanding. Descartes thus mingles many observations with a metaphysic of this nature, and to us the result is hence obscure. In this philosophy the thinking treatment of empiricism is thus predominant, and a similar method has been adopted by philosophers from this time on. To Descartes and others, Philosophy had still the more indefinite significance of arriving at knowledge through thought, reflection, and reasoning. Speculative cognition, the derivation from the Notion, the free independent development of the matter itself, was first introduced by Fichte, and consequently what is now called philosophic knowledge is not yet separated in Descartes from the rest of scientific knowledge. In those times all the knowledge of mankind was called philosophy; in Descartes’ metaphysics we thus saw quite empirical reflection and reasoning from particular grounds, from experiences, facts, phenomena, being brought into play in the naivest manner, and one has no sense of speculation in the matter. The strictly scientific element here really consisted mainly in the method of proof as it has long been made use of in geometry, and in the ordinary method of the formal logical syllogism. Hence it likewise happens that Philosophy, which ought to form a totality of the sciences, begins with logic and metaphysics; the second part is composed of ordinary physics and mathematics, mingled no doubt with metaphysical speculations, and the third part, ethics, deals with the nature of man, his duties, the state, the citizen. And this is the case with Descartes. The first part of the _Principia philosophiæ_ treats _De principiis cognitionis humanæ_, the second _De principiis rerum materialium_. This natural philosophy, as a philosophy of extension, is, however, none other than what a quite ordinary physics or mechanics might at that time be, and it is still quite hypothetical; we, on the other hand, accurately distinguish empirical physics and natural philosophy, even though the first likewise pertains to thought.