Reply Obj. 2:  Something is required for the perfection of knowledge, that is not requisite for the perfection of love.  For knowledge belongs to the reason, whose function it is to distinguish things which in reality are united, and to unite together, after a fashion, things that are distinct, by comparing one with another.  Consequently the perfection of knowledge requires that man should know distinctly all that is in a thing, such as its parts, powers, and properties.  On the other hand, love is in the appetitive power, which regards a thing as it is in itself:  wherefore it suffices, for the perfection of love, that a thing be loved according as it is known in itself.  Hence it is, therefore, that a thing is loved more than it is known; since it can be loved perfectly, even without being perfectly known.  This is most evident in regard to the sciences, which some love through having a certain general knowledge of them:  for instance, they know that rhetoric is a science that enables man to persuade others; and this is what they love in rhetoric.  The same applies to the love of God.

Reply Obj. 3:  Even natural love, which is in all things, is caused by a kind of knowledge, not indeed existing in natural things themselves, but in Him Who created their nature, as stated above (Q. 26, A. 1; cf.  I, Q. 6, A. 1, ad 2). ________________________

THIRD ARTICLE [I-II, Q. 27, Art. 3]

Whether Likeness Is a Cause of Love?

Objection 1:  It would seem that likeness is not a cause of love.  For the same thing is not the cause of contraries.  But likeness is the cause of hatred; for it is written (Prov. 13:10) that “among the proud there are always contentions”; and the Philosopher says (Ethic. viii, 1) that “potters quarrel with one another.”  Therefore likeness is not a cause of love.

Obj. 2:  Further, Augustine says (Confess. iv, 14) that “a man loves in another that which he would not be himself:  thus he loves an actor, but would not himself be an actor.”  But it would not be so, if likeness were the proper cause of love; for in that case a man would love in another, that which he possesses himself, or would like to possess.  Therefore likeness is not a cause of love.

Obj. 3:  Further, everyone loves that which he needs, even if he have it not:  thus a sick man loves health, and a poor man loves riches.  But in so far as he needs them and lacks them, he is unlike them.  Therefore not only likeness but also unlikeness is a cause of love.

Obj. 4:  Further, the Philosopher says (Rhet. ii, 4) that “we love those who bestow money and health on us; and also those who retain their friendship for the dead.”  But all are not such.  Therefore likeness is not a cause of love.

On the contrary, It is written (Ecclus. 13:19):  “Every beast loveth its like.”