6. But, further, although one who loves or one who knows is a substance, and knowledge is a substance, and love is a substance, but he that loves and love, or, he that knows and knowledge, are spoken of relatively to each other, as are friends: yet mind or spirit are not relatives, as neither are men relatives: nevertheless he that loves and love, or he that knows and knowledge, cannot exist separately from each other, as men can that are friends. Although it would seem that friends, too, can be separated in body, not in mind, in as far as they are friends: nay, it can even happen that a friend may even also begin to hate a friend and on this account cease to be a friend while the other does not know it, and still loves him. But if the love with which the mind loves itself ceases to be, then the mind also will at the same time cease to love. Likewise, if the knowledge by which the mind knows itself ceases to be, then the mind will also at the same time cease to know itself. Just as the head of anything that has a head is certainly a head, and they are predicated relatively to each other, although they are also substances: for both a head is a body, and so is that which has a head; and if there be no head, then neither will there be that which has a head. Only these things can be separated from each other by cutting off, those cannot.