Placaeus: fallen man could not sin if he willed as he ought, so the power not to sin belongs to nature
Josué de la Place seems to go further, though in substance he arrives at the same place. However deep man's corruption, he teaches, man could avoid sin if he willed to, that is, if his will were set against sinning as it ought to be. So the ability not to sin, given a serious and proper willing, is to be credited to nature and not to grace.
He holds that even corrupt man has this ability: he can sin if he wishes, and he can also not sin, provided his will recoils from sin as it should. 'So,' he says, 'those who credit grace with the ability not to sin, on the condition that the will were rightly set against sinning, seem not to have weighed the nature of things well. It belongs rather to nature, which makes the notions of the involuntary and of sin conflict with each other.'
From this he concludes that it is useless to cite against us the scriptures that grant man the ability to do good if he wills, meaning if he wills as he should. Treatise on free choice, chapter 4.
Latin
XXIX. Josue Placaeus vero videtur aliquid amplius dicere, sed tamen quod eodem redit, quantum ad summam rei. Docet enim, quantacunque sit hominis corruptio, illum posse non peccare si vellet, & si ad non peccandum voluntas ejus esset, uti decet, comparata. Adeoque facultatem non peccandi in homine, si istud serio velit & ut oportet, non ascribendam esse gratiae, sed naturae. Affirmat enim eam facultatem etiam homini corrupto inesse, ut non modo peccare possit si velit, sed etiam non peccare, si quidem, uti par est, a peccato voluntas ejus abhorreret. Quare, inquit, non bene considerasse rerum naturas videntur illi qui facultatem non peccandi, si ad non peccandum, uti decet, comparata esset voluntas, gratiae tribuunt, cum sit potius ascribenda naturae, qua fit ut involuntarii & peccati rationes inter se pugnent. Unde colligit frustra nobis objici ea scripturae loca, quibus tribuit eam facultatem homini, ut possit bene agere si velit: nempe quomodo eum decet velle. Tractatu de libero arbitrio cap. 4.