Bonum est propria causa amoris quia amoris proprium obiectum est bonum; quia, ut dictum est, amor importat quandam connaturalitatem vel complacentiam amantis ad amatum; unicuique autem est bonum id quod est sibi connaturale et proportionatum.
Good is the proper cause of love because the proper object of love is the good; since, as stated above (q26, a1,a2), love implies a certain connaturalness, or fitting pleasure, of the lover for the thing beloved; and to everything, that thing is a good, which is akin and [fittingly] proportionate to it.
Amor ad appetitivam potentiam pertinet, quae est vis passiva. Unde obiectum eius comparatur ad ipsam sicut causa motus vel actus ipsius. Oportet igitur ut illud sit proprie causa amoris quod est amoris obiectum.
Love belongs to the appetitive power which is a passive faculty. Wherefore its object stands in relation to it as the cause of its movement or act. Therefore the cause of love must needs be love's object.
Malum nunquam amatur nisi sub ratione boni, scilicet inquantum est secundum quid bonum, et apprehenditur ut simpliciter bonum. Et sic aliquis amor est malus, inquantum tendit in id quod non est simpliciter verum bonum.
Evil is never loved except under the formal aspect of good, that is to say, insofar as it is good in some respect, but is [instead] considered as being good simply. And thus a certain love is evil, insofar as it tends to that which is not simply a true good.
Pulchrum est idem bono, sola ratione differens. Cum enim bonum sit quod omnia appetunt, de ratione boni est quod in eo quietetur appetitus; sed ad rationem pulchri pertinet quod in eius aspectu seu cognitione quietetur appetitus.
The beautiful is the same as the good, and they differ in formal aspect only. For since good is what all seek, the formal aspect of good is that which calms the appetite; while the formal aspect of the beautiful is that which calms the appetite by its [merely] being seen or known.
Unde et illi sensus praecipue respiciunt pulchrum, qui maxime cognoscitivi sunt: scilicet visus et auditus rationi deservientes.
Consequently those senses chiefly regard the beautiful, which are the most cognitive: viz. sight and hearing, as [the senses that are foremost in] attaining the formal aspect.
Dicimus enim pulchra visibilia et pulchros sonos. In sensibilibus autem aliorum sensuum, non utimur nomine pulchritudinis, non enim dicimus pulchros sapores aut odores.
For we speak of beautiful sights and beautiful sounds. But in reference to the other formal objects of (i.e., the other specific things sensed by) the other senses, we do not [customarily] use the expression "beautiful," for we do not speak of beautiful tastes, and beautiful odors.
Et sic patet quod pulchrum addit supra bonum, quendam ordinem ad vim cognoscitivam: ita quod bonum dicatur id quod simpliciter complacet appetitui; pulchrum autem dicatur id cuius ipsa apprehensio placet.
Thus it is evident that beauty adds, on top of goodness, a certain ordination towards cognitive power: thus results the [customary] fact that "good" is spoken of that which simply pleases the appetite; while "beautiful" is spoken of that about which [merely] the apprehension itself is pleasing.