If we imagine that an evil has been brought upon us through the hatred of some person towards whom we have hitherto been moved by no emotion, we shall immediately endeavor to return that evil upon him. If we imagine that any one like ourselves is affected with hatred towards an object like ourselves which we love, we shall hate him. If we imagine that we are beloved by a person without having given any cause for the love we shall love him in return. If we imagine that we have given just cause for love, we shall pride ourselves upon it. This frequently occurs, and we have said that the contrary takes place when we believe that we are hated by another person. This reciprocal love, and consequently this attempt to do good to the person who loves us, and who endeavors to do good to us, is called _thankfulness_ or _gratitude_, and from this we can see how much readier men are to revenge themselves than to return a benefit. If we imagine that we are loved by a person we hate, we shall at the same time be agitated both by love and hatred. If the hatred prevail, we shall endeavor to bring evil upon the person by whom we are loved. This emotion is called Cruelty, especially if it is believed that the person who loves has not given any ordinary reason for hatred. _The "Herd Instinct"_ If we imagine men to love or hate a thing, we shall therefore love or hate it; that is to say, we shall therefore rejoice or be sad at the presence of the thing, and therefore we shall endeavor to do everything which we imagine men[28] will look upon with joy, and, on the contrary, we shall be averse to doing anything to which we imagine men are averse. He who imagines that he affects others with joy or sorrow will necessarily be affected with joy or sorrow. But since man is conscious of himself by means of the emotions by which he is determined to act; therefore if a person has done anything which he imagines will affect others with joy, he also will be affected with joy, accompanied with an idea of himself as its cause; that is to say, he will look upon himself with joy. If, on the other hand, he has done anything which he imagines will affect others with sorrow, he will look upon himself with sorrow. If we imagine that a person loves, desires, or hates a thing which we ourselves love, desire, or hate, we shall on that account love, desire, or hate the thing more steadily. If, on the other hand, we imagine that he is averse to the thing we love or loves the thing to which we are averse, we shall then suffer vacillation of mind. It follows from this proposition that every one endeavors as much as possible to make others love what he loves, and to hate what he hates. Hence the poet says: Speremus pariter, pariter metuamus amantes; Ferreus est, si quis, quod sinit alter, amat.