Psychologia Empirica

[it is the] custom of the learned that what is newly discovered is not admitted until, after some space of time, it has been impugned, brought into odium, and brought to the brink of extirpation: we deemed it inadvisable that the foundations of doctrines most useful to the human race be shaken even in appearance. Wherefore, if anyone should be of too dull a wit to grasp rational psychology, let him set it aside—indeed, if he pleases, let him condemn it—and proceed immediately to practical philosophy, firmly persuaded that he will progress no less along an unhindered path through its spacious field than one to whom it has been granted to know his own soul a priori. Although, in empirical psychology, we deliver nothing but what stands by the certain warrant of experience and what everyone can experience in himself, provided he has raised his faculties to such a degree that they are suited to the exercises required herein; yet, notwithstanding this, having followed the laws of our method, we have arranged the entire doctrine in such an order that some things are deduced from others, and consequent matters are demonstrated from their antecedents. We deemed this to be necessary above all, so that it might be evidently manifest,