Proof.- The effort for self-preservation is nothing else but the essence of the thing in question (III:vii.), which, in so far as it exists such as it is, is conceived to have force for continuing in existence (III:vi.) and doing such things as necessarily follow from its given nature (see the Def. of Appetite, II:ix.Note). But the essence of reason is nought else but our mind, in so far as it clearly and distinctly understands (see the definition in II:xl.Note:ii.); therefore (III:xl.) whatsoever we endeavour in obedience to reason is nothing else but to understand. Again, since this effort of the mind wherewith the mind endeavours, in so far as it reasons, to preserve its own being is nothing else but understanding; this effort at understanding is (IV:xxii.Coroll.) the first and single basis of virtue, nor shall we endeavour to understand things for the sake of any ulterior object (IV:xxv.); on the other hand, the mind, in so far as it reasons, will not be able to conceive any good for itself, save such things as are conducive to understanding.
Prop. XXVII. We know nothing to be certainly good or evil, save such things as really conduce to understanding, or such as are able to hinder us from understanding.
Proof.- The mind, in so far as it reasons, desires nothing beyond understanding, and judges nothing to be useful to itself, save such things as conduce to understanding (by the foregoing Prop.). But the mind (II:xli.&Note) cannot possess certainty concerning anything, except in so far as it has adequate ideas, or (what by II:xl.Note, is the same thing) in so far as it reasons. Therefore we know nothing to be good or evil save such things as really conduce, &c. Q.E.D.
Prop. XXVIII. The mind's highest good is the knowledge of God, and the mind's highest virtue is to know God.
Proof.- The mind is not capable of understanding anything higher than God, that is (I:Def.vi.), than a Being absolutely infinite, and without which (I:xv.) nothing can either be or be conceived; therefore (IV:xxvi., &xxvii.), the mind's highest utility or (IV:Def.i.) good is the knowledge of God. Again, the mind is active, only in so far as it understands, and only to the same extent can it be said absolutely to act virtuously. The mind's absolute virtue is therefore to understand. Now, as we have already shown, the highest that the mind can understand is God; therefore the highest virtue of the mind is to understand or to know God. Q.E.D.
Prop. XXIX. No individual thing, which is entirely different from our own nature, can help or check our power of activity, and absolutely nothing can do us good or harm, unless it has something in common with our nature.
Proof.- The power of every individual thing, and consequently the power of man, whereby he exists and operates, can only be determined by an individual thing (I:xxviii.), whose nature (II:vi.) must be understood through the same nature as that, through which human nature is conceived.
Therefore our power of activity, however it be conceived, can be determined and consequently helped or hindered by the power of any other individual thing, which has something in common with us, but not by the power of anything, of which the nature is entirely different from our own; and since we call good or evil that which is the cause of pleasure or pain (IV:viii.), that is (III:xi.Note), which increases or diminishes, helps or hinders, our power of activity; therefore, that which is entirely, different from our nature can neither be to us good nor bad. Q.E.D.
Prop. XXX. A thing cannot be bad for us through the quality which it has in common with our nature, but it is bad for us in so far as it is contrary to our nature.
Proof.- We call a thing bad when it is the cause of pain (IV:viii.), that is (by the Def., which see in III:xi.Note), when it diminishes or checks our power of action. Therefore, if anything were bad for us through that quality which it has in common with our nature, it would be able itself to diminish or check that which it has in common with our nature, which (III:iv.) is absurd. Wherefore nothing can be bad for us through that quality which it has in common with us, but, on the other hand, in so far as it is bad for us, that is (as we have just shown), in so far as it can diminish or check our power of action, it is contrary to our nature. Q.E.D.
Prop. XXXI. In so far as a thing is in harmony with our nature, it is necessarily good.
Proof.- In so far as a thing is in harmony with our nature, it cannot be bad for it. It will therefore necessarily be either good or indifferent.
If it be assumed that it be neither good nor bad, nothing will follow from its nature (IV:Def.i.), which tends to the preservation of our nature, that is (by the hypothesis), which tends to the preservation of the thing itself; but this (III:vi.) is absurd; therefore, in so far as a thing is in harmony with our nature, it is necessarily good. Q.E.D.
Corollary.- Hence it follows, that, in proportion as a thing is in harmony with our nature, so is it more useful or better for us, and vice versa, in proportion as a thing is more useful for us, so is it more in harmony with our nature. For, in so far as it is not in harmony with our nature, it will necessarily be different therefrom or contrary thereto. If different, it can neither be good nor bad (IV:xxix.); if contrary, it will be contrary to that which is in harmony with our nature, that is, contrary to what is good - in short, bad. Nothing, therefore, can be good, except in so far as it is in harmony with our nature; and hence a thing is useful, in proportion as it is in harmony with our nature, and vice versa. Q.E.D.
Prop. XXXII. In so far as men are a prey to passion, they cannot, in that respect, be said to be naturally in harmony.
Proof. Things, which are said to be in harmony naturally, are understood to agree in power (III:vii.), not in want of power or negation, and consequently not in passion (III:iii.Note); wherefore men, in so far as they are a prey to their passions, cannot be said to be naturally in harmony. Q.E.D.
