X . Two substances are said to be really distinct, when each of them may exist without the other.
Postulates
1st. I request that my readers consider how feeble are the reasons that have hitherto led them to repose faith in their senses, and how uncertain are all the judgments which they afterwards founded on them; and that they will revolve this consideration in their mind so long and so frequently, that, in fine, they may acquire the habit of no longer trusting so confidently in their senses; for I hold that this is necessary to render one capable of apprehending metaphysical truths.
2nd. That they consider their own mind, and all those of its attributes of which they shall find they cannot doubt, though they may have supposed that all they ever received by the senses was entirely false, and that they do not leave off considering it until they have acquired the habit of conceiving it distinctly, and of believing that it is more easy to know than any corporeal object.
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.
4th. That they examine the ideas of those natures which contain in them an assemblage of several attributes, such as the nature of the triangle, that