And because voluntary acts have certain circumstances, according to which we form our judgment concerning them, we must first consider the voluntary and the involuntary, and afterwards, the circumstances of those acts which are found to be voluntary or involuntary.  Under the first head there are eight points of inquiry: 

(1) Whether there is anything voluntary in human acts?

(2) Whether in irrational animals?

(3) Whether there can be voluntariness without any action?

(4) Whether violence can be done to the will?

(5) Whether violence causes involuntariness?

(6) Whether fear causes involuntariness?

(7) Whether concupiscence causes involuntariness?

(8) Whether ignorance causes involuntariness?
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FIRST ARTICLE [I-II, Q. 6, Art. 1]

Whether There Is Anything Voluntary in Human Acts?

Objection 1:  It would seem that there is nothing voluntary in human acts.  For that is voluntary “which has its principle within itself.” as Gregory of Nyssa [Nemesius, De Natura Hom. xxxii.], Damascene (De Fide Orth. ii, 24), and Aristotle (Ethic. iii, 1) declare.  But the principle of human acts is not in man himself, but outside him:  since man’s appetite is moved to act, by the appetible object which is outside him, and is as a “mover unmoved” (De Anima iii, 10).  Therefore there is nothing voluntary in human acts.

Obj. 2:  Further, the Philosopher (Phys. viii, 2) proves that in animals no new movement arises that is not preceded by a motion from without.  But all human acts are new, since none is eternal.  Consequently, the principle of all human acts is from without:  and therefore there is nothing voluntary in them.

Obj. 3:  Further, he that acts voluntarily, can act of himself.  But this is not true of man; for it is written (John 15:5):  “Without Me you can do nothing.”  Therefore there is nothing voluntary in human acts.

On the contrary, Damascene says (De Fide Orth. ii) that “the voluntary is an act consisting in a rational operation.”  Now such are human acts.  Therefore there is something voluntary in human acts.

I answer that, There must needs be something voluntary in human acts.  In order to make this clear, we must take note that the principle of some acts or movements is within the agent, or that which is moved; whereas the principle of some movements or acts is outside.  For when a stone is moved upwards, the principle of this movement is outside the stone:  whereas when it is moved downwards, the principle of this movement is in the stone.  Now of those things that are moved by an intrinsic principle, some move themselves, some not.  For since every agent or thing moved, acts or is moved for an end, as stated above (Q. 1, A. 2); those are perfectly moved by an intrinsic principle, whose intrinsic principle is one not only of movement but of movement for an end.