I answer that, Compulsion or violence is twofold. One is the cause of absolute necessity, and violence of this kind the Philosopher calls (Ethic. iii, 1) "violent simply," as when by bodily strength one forces a person to move; the other causes conditional necessity, and the Philosopher calls this a "mixed violence," as when a person throws his merchandise overboard in order to save himself. In the latter kind of violence, although the thing done is not voluntary in itself, yet taking into consideration the circumstances of place and time it is voluntary. And since actions are about particulars, it follows that it is voluntary simply, and involuntary in a certain respect (Cf. FS, Question [6], Article [6]). Wherefore this latter violence or compulsion is consistent with consent, but not the former. And since this compulsion results from one's fear of a threatening danger, it follows that this violence coincides with fear which, in a manner, compels the will, whereas the former violence has to do with bodily actions. Moreover, since the law considers not merely internal actions, but rather external actions, consequently it takes violence to mean absolute compulsion, for which reason it draws a distinction between violence and fear. Here, however, it is a question of internal consent which cannot be influenced by compulsion or violence as distinct from fear. Therefore as to the question at issue compulsion and fear are the same. Now, according to lawyers fear is "the agitation of the mind occasioned by danger imminent or future" (Ethic. iii, 1).
This suffices for the Replies to the Objections; for the first set of arguments consider the first kind of compulsion, and the second set of arguments consider the second.