lutely impossible; for it is evident that the first terms that we wished to define would imply precedents to serve for their explanation, and that in the same manner, the first propositions that we wished to prove would imply others which had preceded them; and thus it is clear that we should never reach the first.
Thus, in pushing our researches further and further, we arrive necessarily at primitive words which can no longer be defined, and at principles so clear that we can find no others that can serve as a proof of them.
Hence it appears that men are naturally and immutably impotent to treat of any science so that it may be in an absolutely complete order.
But it does not thence follow that we should abandon every kind of order.
For there is one, and it is that of geometry, which is in truth inferior in that it is less convincing, but not in that it is less certain. It does not define every thing and does not prove every thing, and it is in this that it is inferior; but it assumes nothing but things clear and constant by natural enlightenment, and this is why it is perfectly true, nature sustaining it in default of discourse.
This order, the most perfect of any among men, consists not at all in defining every thing or in demonstrating every thing, nor in defining nothing or in demonstrating nothing, but in adhering to this middle course of not defining things clear and understood by all mankind, and of defining the rest; of not proving all the things known to mankind, and of proving all the rest. Against this order those sin alike who undertake to define everything and to prove every thing, and who neglect to do it in those things which are not evident of themselves.
This is what is perfectly taught by geometry. She does not define any of these things, space, time, motion, number, equality, and similar things which exist in great number, because these terms so naturally designate the things that they mean, to those who understand the language, that their elucidation would afford more obscurity than instruction.
For there is nothing more feeble than the discourse of those who wish to define these primitive words. What neces-
