To discover the true origin of morals, and of that love or hatred which arises from mental qualities, we must take the matter pretty deep, and compare some principles which have been already examined and explained. We may begin with considering anew the nature and force of _sympathy_. The minds of all men are similar in their feelings and operations; nor can any one be actuated by any affection of which all others are not in some degree susceptible. As in strings equally wound up, the motion of one communicates itself to the rest, so all the affections readily pass from one person to another, and beget correspondent movements in every human creature. When I see the _effects_ of passion in the voice and gesture of any person, my mind immediately passes from these effects to their causes, and forms such a lively idea of the passion as is presently converted into the passion itself. In like manner, when I perceive the causes of any emotion, my mind is conveyed to the effects, and is actuated with a like emotion. Were I present at any of the more terrible operations of surgery, 'tis certain that, even before it begun, the preparation of the instruments, the laying of the bandages in order, the heating of the irons, with all the signs of anxiety and concern in the patient and assistants, would have a great effect upon my mind, and excite the strongest sentiments of pity and terror. No passion of another discovers itself immediately to the mind. We are only sensible of its causes or effects. From _these_ we infer the passion; and consequently _these_ give rise to our sympathy.