423.  Let something first be said about the conjunction of the understanding and the will, and its being the same thing as the conjunction of good and truth, that being the conjunction that is effected in the world of spirits.  Man has an understanding and a will.  The understanding receives truths and is formed out of them, and the will receives goods and is formed out of them; therefore whatever a man understands and thinks from his understanding he calls true, and whatever a man wills and thinks from his will he calls good.  From his understanding man can think and thus perceive both what is true and what is good; and yet he thinks what is true and good from the will only when he wills it and does it.  When he wills it and from willing does it, it is both in his understanding and in his will, consequently in the man.  For neither the understanding alone nor the will alone makes the man, but the understanding and will together; therefore whatever is in both is in the man, and is appropriated to him.  That which is in the understanding alone is in man, and yet not really in him; it is only a thing of his memory, or a matter of knowledge in his memory about which he can think when in company with others and outside of himself, but not in himself; that is, about which he can speak and reason, and can simulate affections and gestures that are in accord with it.

424.  This ability to think from the understanding and not at the same time from the will is provided that man may be capable of being reformed; for reformation is effected by means of truths, and truths pertain to the understanding, as just said.  For in respect to his will man is born into every evil, and therefore of himself wills good to no one but himself; and one who wills good to himself alone delights in the misfortunes that befall another, especially when they tend to his own advantage; for his wish is to divert to himself the goods of all others, whether honors or riches, and so far as he succeeds in this he inwardly rejoices.  To the end that this will of man may be corrected and reformed, an ability to understand truths, and an ability to subdue by means of truths the affections of evil that spring from the will, are given to man.  This is why man has this ability to think truths with his understanding, and to speak them and do them.  But until man is such that he wills truths and does them from himself, that is, from the heart, he is not able to think truths from his will.  When he becomes such, whatever he thinks from his understanding belongs to his faith, and whatever he thinks from his will belongs to his love; and in consequence his faith and his love, like his understanding and his will, are conjoined in him.