Necessity of sinning does not remove essential liberty
Thesis XXXIX. Without grace man is the servant of sin, as Scripture says, and whatever he does he cannot help sinning. Yet this necessity of doing evil does not take away the natural freedom of his choice. The freedom that belongs essentially to every agent with intellect and will does not consist in being indifferent between acting well and acting badly, with an equal power for either. Otherwise neither the demons in hell nor the angels in heaven would act freely, since the demons are fixed on doing evil and the angels, conversely, on doing good.
That natural freedom of choice consists rather in acting without compulsion and without any brute impulse of nature, choosing what one pleases and thinks fit after a prior judgement and deliberation of the mind. So this freedom is opposed to coercion and to natural or brute determination, but not at all to the bondage of sin. That bondage does not stop a man, when he sins, from acting deliberately and at the dictate of his own reason, without any coercion and without natural or brute determination.
Latin
XXXIX. Quamvis enim absente gratia, Homo sit peccati servus, ut scriptura loquitur, & quicquid agat non possit nisi peccare: ista tamen male agendi necessitas naturalem arbitrii ejus libertatem non tollit. Libertas enim illa quae essentialis est omni agenti intellectu & voluntate praedito, non consistit in eo ut quis indifferens sit ad bene vel male agendum, & parem ad utrumque facultatem habeat. Alioqui nec daemones in inferno, nec Angeli in coelo libere operarentur, cum illi quidem ad male agendum, hi vero contra ad bene agendum sint determinati. Verum in eo sita est ista naturalis arbitrii libertas, ut quis agat non coactus, nec etiam bruto naturae impulsu, sed praevio mentis judicio & deliberatione eligat quod ipsi lubet & videtur. Adeoque libertas illa opponitur coactioni, & naturali, seu brutae determinationi, minime vero servituti peccati, quae non obstat quominus homo, dum peccat, deliberate agat, & ex rationis propriae dictamine, absque ulla coactione, & naturali seu bruta determinatione.