We come now to explain the direct passions, or the impressions, which arise immediately from good or evil, from pain or pleasure.  Of this kind are, desire and aversion, grief and joy, hope and fear.

Of all the immediate effects of pain and pleasure, there is none more remarkable than the will; and though properly speaking, it be not comprehended among the passions, yet as the full understanding of its nature and properties, is necessary to the explanation of them, we shall here make it the subject of our enquiry.  I desire it may be observed, that by the will, I mean nothing but the internal impression we feel and are conscious of, when we knowingly give rise to any new motion of our body, or new perception of our mind.  This impression, like the preceding ones of pride and humility, love and hatred, it is impossible to define, and needless to describe any farther; for which reason we shall cut off all those definitions and distinctions, with which philosophers are wont to perplex rather than dear up this question; and entering at first upon the subject, shall examine that long disputed question concerning liberty and necessity; which occurs so naturally in treating of the will.

It is universally acknowledged, that the operations of external bodies are necessary, and that in the communication of their motion, in their attraction, and mutual cohesion, there are nor the least traces of indifference or liberty.  Every object is determined by an absolute fate toa certain degree and direction of irs motion, and can no more depart from that precise line, in which it moves, than it can convert itself into an angel, or spirit, or any superior substance.  The actions, therefore, of matter are to be regarded as instances of necessary actions; and whatever is in this respect on the same footing with matter, must be acknowledged to be necessary.  That we may know whether this be the case with the actions of the mind, we shall begin with examining matter, and considering on what the idea of a necessity in its operations are founded, and why we conclude one body or action to be the infallible cause of another.

It has been observed already, that in no single instance the ultimate connexion of any objects is discoverable, either by our senses or reason, and that we can never penetrate so far into the essence and construction of bodies, as to perceive the principle, on which their mutual influence depends.  It is their constant union alone, with which we are acquainted; and it is from the constant union the necessity arises.  If objects had nor an uniform and regular conjunction with each other, we should never arrive at any idea of cause and effect; and even after all, the necessity, which enters into that idea, is nothing but a determination of the mind to pass from one object to its usual attendant, and infer the existence of one from that of the other.  Here then are two particulars, which we are to consider as essential to necessity, viz, the constant union