We call a thing good which contributes to the preservation of our being, and we call a thing evil if it is an obstacle to the preservation of our being; that is to say, a thing is called by us good or evil as it increases or diminishes, helps or restrains, our power of action. In so far, therefore, as we perceive that any object affects us with joy or sorrow do we call it good or evil, and therefore the knowledge of good or evil is nothing but an idea of joy or sorrow which necessarily follows from the emotion itself of joy or sorrow. But this idea is united to the emotion in the same way as the mind is united to the body, or, in other words, this idea is not actually distinguished from the emotion itself; that is to say, it is not actually distinguished from the idea of the modification of the body, unless in conception alone. This knowledge, therefore, of good and evil is nothing but the emotion itself of joy and sorrow in so far as we are conscious of it. _The Control of the Emotions_ An emotion, in so far as it is related to the mind, is an idea by which the mind affirms a greater or less power of existence for its body than the body possessed before. Whenever, therefore, the mind is agitated by any emotion, the body is at the same time affected with a modification by which its power of action is increased or diminished. Again, this modification of the body receives from its own cause a power to persevere in its own being, a power, therefore, which cannot be restrained nor removed unless by a bodily cause affecting the body with a modification contrary to the first, and stronger than it. Thus the mind is affected by the idea of a modification stronger than the former and contrary to it; that is to say, it will be affected with an emotion stronger than the former and contrary to it, and this stronger emotion will exclude the existence of the other or remove it. Thus an emotion cannot be restrained nor removed unless by an opposed and stronger emotion. An emotion, in so far as it is related to the mind, cannot be restrained nor removed unless by the idea of a bodily modification opposed to that which we suffer and stronger than it. For the emotion which we suffer cannot be restrained nor removed unless by an opposed and stronger emotion; that is to say, it cannot be removed unless by the idea of a bodily modification stronger than that which affects us, and opposed to it. The force and increase of any passion and its perseverance in existence are limited by the power of an external cause compared with our own power and therefore the other actions or power of a man may be so far surpassed by force of some passion or emotion, that the emotion may obstinately cling to him.