Hoc modo cessatio ab actu causat corruptionem vel diminutionem habituum, inquantum scilicet removetur actus qui prohibebat causas corrumpentes vel diminuentes habitum, quia habitus per se corrumpuntur vel diminuuntur ex contrario agente; unde quorumcumque habituum contraria subcrescunt per temporis tractum, quae oportet subtrahi per actum ab habitu procedentem: huiusmodi habitus diminuuntur, vel etiam tolluntur totaliter, per diuturnam cessationem ab actu, ut patet et in scientia et in virtute.
The destruction or diminution of a habit results through cessation from act, insofar, to wit, as we cease from exercising an act which overcame the causes that destroyed or weakened that habit because habits are destroyed or diminished directly through some contrary agency; consequently all habits that are gradually undermined by contrary agencies which need to be counteracted by acts proceeding from those habits, are diminished or even destroyed altogether by long cessation from act, as is clearly seen in the case both of science and of virtue.
Cum igitur homo cessat ab usu intellectualis habitus, insurgunt imaginationes extraneae, et quandoque ad contrarium ducentes; ita quod, nisi per frequentem usum intellectualis habitus, quodammodo succidantur vel comprimantur, redditur homo minus aptus ad recte iudicandum, et quandoque totaliter disponitur ad contrarium. Et sic per cessationem ab actu diminuitur, vel etiam corrumpitur intellectualis habitus.
When man ceases to make use of his intellectual habits, strange fancies, sometimes in opposition to them, arise in his imagination; so that unless those fancies be, as it were, cut off or kept back by frequent use of his intellectual habits, man becomes less fit to judge aright, and sometimes is even wholly disposed to the contrary. And thus the intellectual habit is diminished or even wholly destroyed by cessation from act.
Pars intellectiva animae secundum se est supra tempus, sed pars sensitiva subiacet tempori. Et ideo per temporis cursum, transmutatur quantum ad passiones appetitivae partis et etiam quantum ad vires apprehensivas. Unde philosophus dicit, in IV Physic., quod tempus est causa oblivionis.
The intellectual part of the soul, considered in itself, is above time, but the sensitive part is subject to time, and therefore in course of time it undergoes change as to the passions of the sensitive part, and also as to the powers of apprehension. Hence the Philosopher says (Phys. iv. text. 117) that time makes us forget.
Philosophus, in libro de Longit. et Brevit. vitae, dicit quod corruptio scientiae non solum est deceptio, sed etiam oblivio. Et in VIII Ethic. dicitur quod multas amicitias inappellatio dissolvit.
The Philosopher says (De Long. et Brev. Vitae ii) that not only "deception," but also "forgetfulness, is the corruption of science." Moreover he says (Ethic. viii, 5) that "want of intercourse has dissolved many a friendship."