Metaphysics of the Music, part 18
For all its similarities with Kant’s idealistic aesthetics, there is nonetheless an intractable, objective or mind-independent character to Thomas’s conception of beauty. The more beauty a thing has the more existence or being will be implicated in that beauty. One aspect to this principle for St. Thomas is his definition of beauty as “that which pleases when seen” (ST1.5.4 ad 1). In direct contrast to Kant, therefore, Thomas establishes as one of the defining features of beauty the pleasure or delight the object of beauty is able to bestow on its perceiver through the senses, which makes beauty at some level presuppose the existence of a perceiver-independent object capable of acting on the senses in this aesthetically pleasing manner. For Thomas, human sense faculties have as their proper activity and end the perception of sensible objects, especially beautiful sensible objects, and aesthetic pleasure or delight consists in this activity being brought to completion—that is to say, in the sensible properties of the object of beauty first stimulating and gratifying the senses, and in their turn effecting a corresponding intellectual apprehension of and satisfaction in the form or internal structure of the physical object. In this manner a harmonious, pleasing, and nature-fulfilling correspondence is established between the object and the perceiving subject and between the subject’s own perceptual and intellective faculties.
 “[P]ulchra enim dicuntur quae visa placent.” Although Thomas’s definition emphasizes visual beauty, Santoro-Brienza makes the point that “visio is further qualified as apprehensio. Sight stands for all perception in general, but particularly for the perception of sight and hearing, and not for taste, touch, and smell, if reference is to beauty.” Santoro-Brienza, “Art and Beauty,” 69. As for Thomas’s above definition of beauty in terms of “that which pleases when seen,” there has been some discussion whether or not Thomas is here to be understood as stating his own personal view on the matter. Eco, in a lengthy note in the bibliography of his Art and Beauty in the Middle Ages, takes Maritain in his Art and Scholasticism to task, lamenting that “[e]xpressions such as pulchrum est id quod placet are accepted as authentic Thomistic formulae by people who do not care, or perhaps are not aware, that this is a definition devised by Maritain himself. What Aquinas actually wrote was pulchrum dicuntur quae visa placent. The difference is considerable. Maritain’s proposition is a dogmatic attempt to define once and for all the ontological character of beauty. Aquinas’s is more like a sociological finding. It means, ‘Things which give pleasure when they are perceived are called beautiful’, and this is to introduce the problem, not solve it.” Eco, Art and Beauty in the Middle Ages, 128. Murphy, however, has taken Eco to task in his turn: “A grammatical point can be made in defence of Maritain’s interpretation: how does St Thomas use the phrase dicuntur elsewhere? Each of his arguments for the existence of God concludes with a similar phrase, e.g., ‘one is bound to arrive at some first cause… and this is what everybody understands by God.’ Whilst distinguishing finite being from the self-subsistent being of God, St Thomas says: ‘the first cause is above being insofar as it is infinite being; ‘being’ (ens), however is called that which participates in being in a finite way, and this being is proportionate to our intellect.’… One would hesitate to conclude that this is the product of a sociological survey. Eco hangs too much on the use of the present passive plural. St Thomas uses the present passive singular and the gerundive, (dicitur, dicendum) more often. This is because, in the scholastic Quaestio, the master’s reply to the ‘problem’ set quaeritur, ‘it is asked’) usually commences with dicendum, ‘it ought to be said’. But the meaning of the verb appears to be interchangeable. Thus, St Thomas writes elsewhere: ‘let that be called beauty, the very perception of which pleases.’ (‘pulchrum autem dicitur id cuius ipsa apprehensio placet.’ [ST1-2.27.1 ad 3]).” Murphy, Christ the Form of Beauty, 209. G.B. Phelan has also defended the formula “pulchrum est quod visum placet” as a valid though not complete interpretation of Aquinas’s own definition “pulchra dicuntur quae visa placet.” Phelan, “The Concept of Beauty in St. Thomas Aquinas,” 174.
 Santoro-Brienza, “Art and Beauty,” 70.