Kant felt himself to be the finisher of skepticism; but this was chiefly because he had received the strongest impulse to the development of his critique of knowledge from Hume’s inquiries concerning causation.  Brought up in the dogmatic rationalism of the Wolffian school, to which he remained true for a considerable period as a teacher and writer (till about 1760), although at the same time he was inquiring with an independent spirit, Kant was gradually won over through the influence of the English philosophy to the side of empirical skepticism.  Then—­as the result, no doubt, of reading the Nouveaux Essais of Leibnitz, published in 1765—­he returned to rationalistic principles, until finally, after a renewal of empirical influences,[1] he took the position crystallized in the Critique of Pure Reason, 1781, which, however, experienced still other, though less considerable, changes in the sequel, just as in itself it shows the traces of previous transformations.

[Footnote 1:  Cf.  H. Vaihinger’s Kommentar zu Kants Kritik der reinen Vernunft, vol. i., 1881, pp. 48-49.  This is a work marked by acuteness, great industry, and an objective point of view which merits respect.  The second volume, which treats of the Transcendental Aesthetic, appeared in 1892.]

It would be a most interesting task to trace in the writings which belong to Kant’s pre-critical period the growth and development of the fundamental critical positions.  Here, however, we can only mention in passing the subjects of his reflection and some of the most striking anticipations and beginnings of his epoch-making position.  Even his maiden work, Thoughts on the True Estimation of Vis Viva, 1747, betokens the mediating nature of its author.  In this it is argued that when men of profound and penetrating minds maintain exactly opposite opinions, attention must be chiefly directed to some intermediate principle to a certain degree compatible with the correctness of both parties.  The question under discussion was whether the measure of vis viva is equal, as the Cartesians thought, to the product of the mass into the velocity, or, according to the Leibnitzians, to the product of the mass into the square of the velocity.  Kant’s unsatisfactory solution of the problem—­the law of Descartes holds for dead, and that of Leibnitz for living forces—­drew upon him the derision of Lessing, who said that he had endeavored to estimate living forces without having tested his own.  A similar tendency toward compromise—­this time it is a synthesis of Leibnitz and Newton—­is seen in his Habilitationsschrift, Principiorum Primorum Cognitionis Metaphysicae Nova Dilucidatio, 1755, and in the dissertation Monadologia Physica, 1756.  The former distinguishes between ratio essendi and ratio cognoscendi, rejects the ontological argument, and defends determinism against Crusius on Leibnitzian grounds.  In the Physical