The recent Thomists: efficacious grace as God's physical operation (Estius)
Thesis XXXVI. These recent Thomists locate the aid proper to efficacious grace in a gratuitous and gracious working of God that, properly speaking, produces conversion itself, or any other act of true piety, within a person's free choice. It does so by acting efficiently on the will's very movement, that is, by applying the will itself and determining it to will and to choose. This working is called physical, meaning working in the proper sense, such as is recognized in God with respect to all the other effects that come from him.
Since it is impossible for God to determine the will without its being determined and doing what God applies it to as a secondary cause, it follows that this grace cannot fail to have its effect. 'Hence, on this view, the grace of God is called efficacious with an efficacy not moral but physical, and in the most proper sense.' These are the words of Estius on book 2 of the Sentences, distinction 28, paragraph 2.
Latin
XXXVI. Auxilium autem gratiae efficacis proprium recentiores illi Thomistae constituunt in gratuita & benigna Dei operatione, quae proprie in libero hominis arbitrio operatur ipsam conversionem, seu alium quemcunque actum verae pietatis. Videlicet ipsum voluntatis motum efficienter attingendo, hoc est, voluntatem ipsam applicando & determinando ad volendum & eligendum. Quae operatio Physica vocatur, id est, proprie dicta. Qualis nimirum agnoscitur in Deo ad alios quoscunque effectus ab ipso procedentes. Quoniam vero fieri nequit ut Deus voluntatem determinet, & non ipsa determinetur, agatque id ad quod tanquam causa secunda applicatur a Deo; sequitur, fieri non posse ut gratia ista non habeat suum effectum. Unde hac ratione, juxta hanc sententiam, efficax dicitur Gratia Dei efficacitate non morali, sed physica & propriissime dicta. Quae verba sunt Estii in 2. sentent. dist. 28. paragr. 2.