Non omnis actus habitum auget quia vero usus habituum in voluntate hominis consistit, ut ex supradictis patet: sicut contingit quod aliquis habens habitum non utitur illo, vel etiam agit actum contrarium; ita etiam potest contingere quod utitur habitu secundum actum non respondentem proportionaliter intensioni habitus.
It is not every act that increases a habit because use of habits depends on the will, as was shown above (q50 a5): just as one who has a habit may fail to use it or may act contrary to it; so may he happen to use the habit by performing an act that is not in proportion to the intensity of the habit.
Si igitur intensio actus proportionaliter aequetur intensioni habitus, vel etiam superexcedat, quilibet actus vel auget habitum, vel disponit ad augmentum ipsius (ut loquamur de augmento habituum ad similitudinem augmenti animalis).
Accordingly, if the intensity of the act correspond in proportion to the intensity of the habit, or even surpass it, every such act either increases the habit or disposes to an increase thereof (if we may speak of the increase of habits as we do of the increase of an animal).
Si vero intensio actus proportionaliter deficiat ab intensione habitus, talis actus non disponit ad augmentum habitus, sed magis ad diminutionem ipsius.
If, however, the act falls short of the intensity of the habit, such an act does not dispose to an increase of that habit, but rather to a lessening thereof.
"Similes actus similes habitus causant", ut dicitur in II Ethic.
"Like acts cause like habits" (Ethic. ii, 1,2).
Sed, sicut dicitur in II Ethic., aliqui actus ab habitu procedentes diminuunt ipsum, utpote cum negligenter fiunt.
But according to Ethic. ii, 2, some acts lessen the habit whence they proceed, for instance if they be done carelessly.