With regard to good and evil, these terms indicate nothing positive in things considered in themselves, nor are they anything else than modes of thought, or notions which we form from the comparison of one thing with another. For one and the same thing may at the same time be both good and evil or indifferent. Music, for example, is good to a melancholy person, bad to one mourning, while to a deaf man it is neither good nor bad. But although things are so, we must retain these words. For since we desire to form for ourselves an idea of man upon which we may look as a model of human nature, it will be of service to us to retain these expressions in the sense I have mentioned.
By good, therefore, I understand in the following pages everything which we are certain is a means by which we may approach nearer and nearer to the model of human nature we set before us. By evil, on the contrary, I understand everything which we are certain hinders us from reaching that model. Again, I shall call men more or less perfect or imperfect in so far as they approach more or less nearly to this same model. For it is to be carefully observed, that when I say that an individual passes from a less to a greater perfection and vice versa, I do not understand that from one essence or form he is changed into another (for a horse, for instance, would be as much destroyed if it were changed into a man as if it were changed into an insect), but rather we conceive that his power of action, in so far as it is understood by his own nature, is increased or diminished. Finally, by perfection generally, I understand, as I have said, reality; that is to say, the essence of any object in so far as it exists and acts in a certain manner, no regard being paid to its duration. For no individual thing can be said to be more perfect because for a longer time it has persevered in existence; inasmuch as the duration of things cannot be determined by their essence, the essence of things involving no fixed or determined period of existence; any object, whether it be more or less perfect, always being able to persevere in existence with the same force as that with which it commenced existence. All things, therefore, are equal in this respect.
Definitions
I.—By good, I understand that which we certainly know is useful to us.
II. By evil, on the contrary, I understand that which we certainly know hinders us from possessing anything that is good.
With regard to these two definitions, see the close of the preceding.
III. I call individual things contingent in so far as we discover nothing, whilst we attend to their essence alone, which necessarily posits their existence or which necessarily excludes it.
IV. I call these individual things possible, in so far as we are ignorant, whilst we attend to the cause from which they must be produced, whether these causes are determined to the production of these things.
V. By contrary emotions, I understand in the following pages those which, although they may be of the same kind, draw a man in different directions; such as voluptuousness and avarice, which are both a species of love, and are not contrary to one another by nature, but only by accident.
VI. I here call a thing past or future in so far as we have been or shall be affected by it; for example, in so far as we have seen a thing or are about to see it, in so far as it has strengthened us or will strengthen us, has injured or will injure us. For in so far as we thus imagine it do we affirm its existence; that is to say, the body is affected by no mode which excludes the existence of the thing, and therefore the body is affected by the image of the thing in the same way as if the thing itself were present. But because it generally happens that those who possess much experience hesitate when they think of a thing as past or future, and doubt greatly concerning its issue, therefore the emotions which spring from such images of things are not so constant, but are generally disturbed by the images of other things, until men become more sure of the issue.