A free power can act or not act absolutely speaking, though not in the composite sense under God's efficacious will
Someone may insist that a free power, by its nature, is able to act and not act once everything required for acting is in place. Yet once God's efficacious decree predetermines our free choice to do this particular thing, the will cannot fail to do it, for no one can resist God's will.
Alvarez answers that a free power, by its nature, is able to act and not act, with everything required for acting in place, speaking absolutely and without qualification. It is no absurdity, however, that granted God's efficacious will, it cannot in the composite sense fail to perform the act to which God predetermines it.
Latin
XVI. Si quis autem urgeat esse de ratione potentiae liberae, ut positis omnibus requisitis ad operandum, possit operari & non operari: sed posito Decreto efficaci Dei praedeterminante nostrum liberum arbitrium ad operandum hoc in particulari, non posse voluntatem non operari illud, quia voluntati Dei nullus potest resistere: Respondet, de ratione potentiae liberae esse ut positis omnibus requisitis ad operandum, possit operari & non operari absolute & simpliciter loquendo: non tamen inconveniens esse, quod ex suppositione voluntatis Divinae efficacis, non possit in sensu composito non operari actum illum, ad quem praedeterminatur a Deo.