Jansenius: whatever is voluntary is free, since will and nature are opposite principles
For Jansenius, whatever acts on the judgment of reason acts freely. Since the will is a rational appetite, he holds that will and nature are flatly opposed, and that the will can no more act in the manner of nature than nature can act in the manner of a free cause.
Just as no action of a natural cause can be free, so no action of the will can be natural rather than free. The free therefore reaches exactly as far as the voluntary, and whatever is voluntary is free by that very fact, because the will always and by its essence keeps its own way of acting, distinct from that of nature.
Latin
XXVII. Porro libere juxta ipsum agit, quod ex judicio rationis agit, ac proinde cum voluntas sit appetitus rationalis, existimat voluntatem & naturam esse plane oppositas, neque magis voluntatem agere posse per modum naturae, quam naturam per modum causae liberae. Ideoque sicut nulla actio causae naturalis potest esse libera, ita quoque nullam actionem voluntatis posse naturalem esse, & non liberam: ac proinde liberum aeque late patere atque voluntarium, & quicquid voluntarium est eo ipso liberum esse; quia voluntas semper & essentialiter servat proprium suum operandi modum a natura distinctum.