to enable them to recollect accurately the most fundamental points; that so, on all grave occasions, they might be able to assist themselves on the most important and undeniable principles; in proportion as they devoted themselves to speculations on natural philosophy. And here it is necessary for those who have made sufficient progress in their view of the general question, to recollect the principles laid down as elements of the whole discussion; for we have still greater need of a correct notion of the whole, than we have even of an accurate understanding of the details. We must, therefore, give preference to the former knowledge, and lay up in our memory those principles on which we may rest, in order to arrive at an exact perception of things, and at a certain knowledge of particular objects.
“Now one has arrived at that point when one has thoroughly embraced the conceptions, and, if I may so express myself, the most essential forms, and when one has impressed them adequately on one’s senses.