3rd. That they diligently examine such propositions as are self-evident, which they will find within themselves, as the following:⁠—That the same thing cannot at once be and not be; that nothing cannot be the efficient cause of anything, and the like;⁠—and thus exercise that clearness of understanding that has been given them by nature, but which the perceptions of the senses are wont greatly to disturb and obscure⁠—exercise it, I say, pure and delivered from the objects of sense; for in this way the truth of the following axioms will appear very evident to them.