Ethics, Part V, Proposition 40

In proportion as each thing is more perfect, it possesses more of reality (II. Def. vi.), and, consequently (III. iii. and note), it is to that extent more active and less passive. This demonstration may be reversed, and thus prove that, in proportion as a thing is more active, so is it more perfect. Q.E.D.

Hence it follows that the part of the mind which endures, be it great or small, is more perfect than the rest. For the eternal part of the mind (V. xxiii. xxix.) is the understanding, through which alone we are said to act (III. iii.); the part which we have shown to perish is the imagination (V. xxi.), through which only we are said to be passive (III. iii. and general Def. of the Emotions); therefore, the former, be it great or small, is more perfect than the latter. Q.E.D.

Such are the doctrines which I had purposed to set forth concerning the mind, in so far as it is regarded without relation to the body; whence, as also from I. xxi. and other places, it is plain that our mind, in so far as it understands, is an eternal mode of thinking, which is determined by another eternal mode of thinking, and this other by a third, and so on to infinity; so that all taken together at once constitute the eternal and infinite intellect of God.