Objection 1. It would seem that there is no free-will in the angels. For the act of free-will is to choose. But there can be no choice with the angels, because choice is "the desire of something after taking counsel," while counsel is "a kind of inquiry," as stated in Ethic. iii, 3. But the angels' knowledge is not the result of inquiring, for this belongs to the discursiveness of reason. Therefore it appears that there is no free-will in the angels.
Objection 2. Further, free-will implies indifference to alternatives. But in the angels on the part of their intellect there is no such indifference; because, as was observed already (58, 5), their intellect is not deceived as to things which are naturally intelligible to them. Therefore neither on the part of their appetitive faculty can there be free-will.
Objection 3. Further, the natural endowments of the angels belong to them according to degrees of more or less; because in the higher angels the intellectual nature is more perfect than in the lower. But the free-will does not admit of degrees. Therefore there is no free-will in them.
On the contrary, Free-will is part of man's dignity. But the angels' dignity surpasses that of men. Therefore, since free-will is in men, with much more reason is it in the angels.
I answer that, Some things there are which act, not from any previous judgment, but, as it were, moved and made to act by others; just as the arrow is directed to the target by the archer. Others act from some kind of judgment; but not from free-will, such as irrational animals; for the sheep flies from the wolf by a kind of judgment whereby it esteems it to be hurtful to itself: such a judgment is not a free one, but implanted by nature. Only an agent endowed with an intellect can act with a judgment which is free, in so far as it apprehends the common note of goodness; from which it can judge this or the other thing to be good. Consequently, wherever there is intellect, there is free-will. It is therefore manifest that just as there is intellect, so is there free-will in the angels, and in a higher degree of perfection than in man.
Reply to Objection 1. The Philosopher is speaking of choice, as it is in man. As a man's estimate in speculative matters differs from an angel's in this, that the one needs not to inquire, while the other does so need; so is it in practical matters. Hence there is choice in the angels, yet not with the inquisitive deliberation of counsel, but by the sudden acceptance of truth.
Reply to Objection 2. As was observed already (2), knowledge is effected by the presence of the known within the knower. Now it is a mark of imperfection in anything not to have within it what it should naturally have. Consequently an angel would not be perfect in his nature, if his intellect were not determined to every truth which he can know naturally. But the act of the appetitive faculty comes of this, that the affection is directed to something outside. Yet the perfection of a thing does not come from everything to which it is inclined, but only from something which is higher than it. Therefore it does not argue imperfection in an angel if his will be not determined with regard to things beneath him; but it would argue imperfection in him, were he to be indeterminate to what is above him.
Reply to Objection 3. Free-will exists in a nobler manner in the higher angels than it does in the lower, as also does the judgment of the intellect. Yet it is true that liberty, in so far as the removal of compulsion is considered, is not susceptible of greater and less degree; because privations and negations are not lessened nor increased directly of themselves; but only by their cause, or through the addition of some qualification.
Source: Summa Theologica (New Advent)