Matthew Collings, the art critic, was presenting the Turner Prize TV show. We'd been looking at a couple of the shortlisted works, and now it was time for a commercial break. Collings turned to the camera and said, 'And now, you're going to see some real art.'

I've looked forward to his programmes ever since. This Is Civilization didn't disappoint, and last night was broadcast What Is Beauty?

In a way, the fact that he, an art critic, was even bothering to ask was the most significant thing about the programme. Beauty is not a fashionable subject. I sense the art world is suspicious of it - a trend that reaches back to Kant who argued for a cooler means of aesthetic judgment, and gained strength during the 20th century when beauty's power became morally suspect since even the worst human horrors could be given a beautiful aura, with the right lighting and colour palette. Then there's the association between beauty and divinity, via Platonism. Collings is a master at cutting comments smoothly delivered, and one in this programme was that modern art is not required to be beautiful anymore because modern art galleries themselves are so beautiful - which led me to wonder whether that's why so many modern art galleries outshine much of the art they contain.

He identified 10 'rules' of beauty. Beautiful work reflects nature, embodies simplicity, builds unity, transforms reality, reflects surroundings, animates life, surprises viewers, seeks patterns, wisely selects and shows spontaneity. Our ideas of beauty change over time because what matters to us changes: in beautiful Byzantine art, hierarchy is lauded; in beautiful modern art, random horizontal relationships are celebrated. The same pattern of light will speak of hopes to one generation and horrors to the next.

(If Collings aimed to make a beautiful programme about beauty too, then he conveyed quite a lot more about what he thinks beauty is, as the programme was markedly restless, multi-sensory, self-knowing, appreciative not judgmental, inclusive, naturalistic and hopeful.)

I felt there was an underlying assumption about beauty that ran through the programme, namely that beauty is its own subject. Hence the problem of talking about beauty, because it's impossible to point to a definitive example. It's too self-referential for that, and so the discussion about beauty never ends. However, my sense is that's not actually quite right.

I suspect that beauty is ultimately not its own subject. Rather, something is beautiful because it points to something else. So, the beautiful finally speaks not to our aesthetic judgment, but to our desires. Beauty promises something else we desire, perhaps happiness or insight or fulfillment. This is why we love what is beautiful, and want to commit to it, often by possessing it, or perhaps by trying to define it - though we don't quite know what it will bring. That lack of certainty about what beauty is promising, coupled to the way it speaks to an individual's probably confused loves and longings, is why we will never conclusively agree about what is beautiful. That's the joy of the subject and its intractable nature.

So I would add one more 'rule' to Collings' list, summed up in a word like 'promise' - remembering Stendhal's thought that 'Beauty is nothing other than the promise of happiness.' Or to put it in a more Platonic way, beauty is that which activates our desire for those good things that are at least partially beyond us.

(Image: Presenter Matt Collings in front of the Madonna del Parto, Monterchi, by Piero della Francesca.)