_Explanation._--We have said above, that desire is appetite which is self-conscious, and that appetite is the essence itself of man in so far as it is determined to such acts as contribute to his preservation. But I have taken care to remark that in truth I cannot recognize any difference between human appetite and desire. For whether a man be conscious of his appetite or not, it remains one and the same appetite, and so, lest I might appear to be guilty of tautology, I have not explained desire by appetite, but have tried to give such a definition of desire as would include all the efforts of human nature to which we give the name of appetite, desire, will, or impulse. For I might have said that desire is the essence itself of man in so far as it is considered as determined to any action; but from this definition it would not follow that the mind could be conscious of its desire or appetite, and therefore, in order that I might include the cause of this consciousness, it was necessary to add the words, _in so far as it is conceived as determined to any action by any one of his modifications_. For by a modification of the human essence we understand any constitution of that essence, whether it be innate, whether it be conceived through the attribute of thought alone or of extension alone, or whether it be related to both. By the word "desire," therefore, I understand all the efforts, impulses, appetites, and volitions of a man, which vary according to his changing disposition, and not unfrequently are so opposed to one another that he is drawn hither and thither, and knows not whither he ought to turn. II. _Joy_ is man's passage from a less to a greater perfection. III. _Sorrow_ is man's passage from a greater to a less perfection. _Explanation._--I say passage, for joy is not perfection itself. If a man were born with the perfection to which he passes, he would possess it without the emotion of joy; a truth which will appear the more clearly from the emotion of sorrow, which is the opposite to joy. For that sorrow consists in the passage to a less perfection, but not in the less perfection itself, no one can deny, since in so far as a man shares any perfection he cannot be sad. Nor can we say that sorrow consists in the privation of a greater perfection for privation is nothing. But the emotion of sorrow is a reality, and it therefore must be the reality of the passage to a lesser perfection, or the reality by which man's power of acting is diminished or limited. As for the definitions of cheerfulness, pleasurable excitement, melancholy, and grief, I pass these by, because they are related rather to the body than to the mind, and are merely different kinds of joy or of sorrow. IV. _Astonishment_ is the imagination of an object in which the mind remains fixed because this particular imagination has no connection with others.