Violentia directe opponitur voluntario, sicut etiam et naturali, quia commune est voluntario et naturali quod utrumque sit a principio intrinseco, violentum autem est a principio extrinseco.
Violence is directly opposed to the voluntary, as likewise to the natural, because the voluntary and the natural have this in common, that both are from an intrinsic principle, whereas violence is from an extrinsic principle.
Quantum igitur ad actum qui est immediate ipsius voluntatis, ut supra dictum est, violentia voluntati inferri non potest, unde talem actum violentia involuntarium facere non potest. Sed quantum ad actum imperatum, voluntas potest pati violentiam. Et quantum ad hunc actum, violentia involuntarium facit.
As to the act which proceeds immediately from the will, violence cannot be done to the will, as stated above (q6 a4): wherefore violence cannot make that act involuntary. But as to the commanded act, the will can suffer violence: and consequently in this respect violence causes involuntariness.
Philosophus et Damascenus dicunt, quod "aliquid est involuntarium per violentiam".
The Philosopher (Ethic. iii, 1) and Damascene (De Fide Orth. ii, 24) say that "things done under compulsion are involuntary."