Alvarez II.6: power to the contrary stands with predetermination in the divided sense; the omitter sins by his own fault
In chapter 6 of the same book, answering the second argument, he denies that because God has predetermined someone to will this or that, it is not, absolutely speaking, in his power to will something else, although on the supposition of that divine predetermination it is impossible, in the composite sense, for him to will another object.
In short, he distinguishes between willing and acting on the one hand and being able to will and act on the other. He grants that without that predetermining influence the will never acts, and that with it the will always acts. But he insists that with it the will has the power not to act, and without it the will has the power to act, in the divided sense. On his view the will's power not to act or to act otherwise coexists with the predetermining influence, but the opposite act, or ceasing from the act, does not. Conversely, without that influence the power to act remains in the will, though without it that power is never brought into act.
From this he concludes that someone who omits an act that is commanded omits it freely and sins. Through sufficient help he could have kept the command; by God's mercy he could have had the motion needed to act; and by his own fault he prevented God from giving it to him.
Latin
XXV. Ejusdem vero libri cap. 6. Responsione ad secundum argumentum, ex eo quod Deus aliquem praedeterminavit ad hoc, vel illud volendum, negat sequi quod absolute loquendo, non sit in potestate ejus aliud velle, quamvis ex suppositione divinae illius praedeterminationis, impossibile sit, in sensu composito, quod velit aliud objectum. Uno verbo distinguit inter velle & operari, & posse velle atque operari; & concedit absque influxu illo praedeterminante voluntatem nunquam operari, cum eo vero voluntatem nunquam non operari: sed pertendit, cum illo voluntatem habere potestatem non operandi, & contra absque illo voluntatem habere potestatem operandi, scilicet in sensu diviso. Nimirum ex ejus mente, cum influxu isto praedeterminante stat potentia voluntatis ad non agendum, aut aliter agendum; non stat vero actus oppositus, aut cessatio ab actu. Et vice versa, absque illo influxu manet in voluntate potentia agendi, licet absque illo nunquam in actum educatur. Inde autem colligit fieri ut omittens actum qui est in praecepto libere illum omittat, & peccet; quia per auxilium sufficiens poterat implere illud praeceptum; ex Dei autem misericordia poterat habere motionem illam ad agendum necessariam, sua vero culpa impedivit ne illi donaretur a Deo.