We proceed to the third article thus:

1. It seems that charity is not the form of faith. The species of each thing is derived from its own form. One thing cannot then be the form of another, if the two are distinguished as separate species of one genus. Now in I Cor., ch.13, faith and charity are distinguished as separate species of virtue. Hence charity is not the form of faith.

2. Again, a form and that of which it is the form are in the same thing, since that which arises out of them is one absolutely. But faith is in the intellect, whereas charity is in the will. Hence charity is not the form of faith.

3. Again, the form of a thing is the principle of it. Now in so far as belief is due to the will, its principle would seem to be obedience rather than charity, according to Rom.1:5: "for obedience to the faith among all nations." Obedience is therefore the form of faith, rather than charity.

On the other hand: everything works by means of its form. Now faith worketh by love. The love of charity is therefore the form of faith.

I answer: as we explained in 12ae, Q.1, Art.3, and Q.17, Art.6, voluntary acts take their species from the object to which the will is directed as an end. Now things derive their species from the manner in which a form exists in natural things. The form of any voluntary act is therefore in a sense the end to which it is directed, both because it takes its species from this end, and because its manner of action is bound to correspond to the end proportionately. It is also clear from what we said in the first article that the object of will which the act of faith seeks as an end is the good, and that this good is the divine good, which is the proper object of charity. Charity is accordingly said to be the form of faith, because it is through charity that the act of faith is made perfect, and brought to its form.

On the first point: charity is said to be the form of faith in the sense that it brings the act of faith to its form. There is nothing to prevent one act being brought to its form by different habits, and consequently classified under different species when human actions in general are being discussed, as we said in 12ae, Q.18, Arts.6, 7; Q.61, Art.2.

On the second point: this objection argues from the intrinsic form. Charity is not the intrinsic form of faith, but that which brings the act of faith to its form, as we have said.

On the third point: even obedience itself, like hope and any other virtue which can precede the act of faith, is brought to its true form by charity, as we shall explain in Q.23, Art.8. Charity is named as the form of faith for this reason.