I had a friend once who used to teach philosophy to undergraduates at Cambridge. He told me that for him philosophy was all about the phrase: ' it depends what you mean by....'. He was joking but what he was getting at was that just about anything can be true as long as you make the words fit the meaning that you want them to.
Consider now what might be a good definition of beauty? How about this: 'that which pleases upon being seen (or perceived)? To give it some medieval authenticity here it is in Latin - id quod visum placet. This, is regularly presented as definition of St Thomas Aquinas. I am no philosopher (and so am happy to consider that the problem could be mine), but my first reaction is to be troubled by this definition for two reasons. First is that it didn't seem to take into account the possibility of error in judgement. If I disagree with someone on whether or not something is beautiful (and this has happened plenty of times), and if beauty is an objective quality and not merely a matter of opinion, then one or both of us must be in error. It always seemed to me that the only way of reconciling this with the definition was to say that it depends what you mean by "seen"; and it depends what you mean by "pleased". Maybe this is relying on the fact that to apprehend beauty I have to see in the sense of apprehend clearly, as the pure see; and maybe also it is true if we consider only a genuine pleasure that which is derived from what it truly good. For all I know this definition probably also depends on what you mean by 'that which'. Simple though the expression is, if we have to struggle with the definitions that much to make it fit ordinary experience then does it have any real use? Couldn't someone clever come up with a better definition? Is the goal here to discover truth or to make Thomas Aquinas true I wondered?
The other reason that I struggled with this was that I read this definition first in a book by Jacques Maritain, (Art and Scholasticism, I think) The problem I had with the whole book was that after wading through hundreds of pages of difficult text he finally applied his theories and 'proved', that the work of Picasso, Braques and Severini was beautiful. This seemed so absurd that my reaction was to dismiss Maritain and his book. Clearly I thought, if he should propose such models, he didn't know much about art and didn't understand what constitutes Christian art. Also it soured my opinion on the value of the whole study of aesthetics. Maritain is the great name in the field and in the end all he seems to be doing is using long words to try to justify his personal taste. Like a politician who decides first what he wants to do, and then looks for the persuasive argument afterwards. Here I was trying to learn how to be a good painter, brush in hand, looking for guidance...and in the end, it seems it call comes down to what you like, even for Jacques Maritain. So why bother with all that intellectual stuff at all? I'll just copy what I like. It also put me off reading Aquinas in more depth, because once again, here is a great champion of him
Later in reading Umberto Eco's Art and Beauty in the Middle Ages there is a note in the bibliography at the back that reads as follows in a discussion of Maritain: "Expressions 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 definition was devised by Maritain himself. What Aquinas actually wrote was pulchra 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 that give pleasure when they are perceived are called beautiful', and this is to introduce the problem, not to solve it."
I feel happier just not liking Maritain than I do not liking both him and Aquinas! I always preferred the definition of beauty as 'the radiance of being' or John Paul II's 'the good made visible' anyway (the latter comes from his Letter to Artists). Once we have either of these, then Aquinas's three qualities of beauty: integrity, due proportion and claritas work well..(.he did actually give us these didn't he?).