In 2003 the Investors Chronicle surveyed their readers about whether buying art was a good investment or not.
They concluded that it was the second most important kind of investment, just behind houses and ahead of the stock market.
Turns out they were right – because three years later art prices are still rising. Last summer Gustav Klimt's portrait of Adele Bloch-Bauer sold for £73 million, the most expensive painting ever sold in a private sale.
Prices of old masters have risen by 50 percent since 1995, and those of contemporary art by 55 percent.
There is a fashion for art-only investment funds, where a group pools their money to buy pieces they think will increase in value.
Banks such as UBS and Citigroup include 'art banking' advice as one of their 'wealth management' services. (Before you rush out to spend your savings, bear in mind the minimum investment in art funds is around £150,000).
Back in the real world, the pictures most of us have on our walls are prints, which typically cost about £5.
The whole point of prints is to look identical to the original. So why is the original worth so much more?
OK, we're probably missing out on some of the fine details of the brush strokes, but that doesn't seem quite enough to pay an extra £5 million for.
The difference between a 'real' Monet and the copy of a Monet on your wall is absolutely nothing to do with what it looks like, even though you might think that's what art is all about. It's to do with what it can be sold for.
Basically it's a con trick – originals are worth fortunes because people are willing to pay fortunes for them, and they believe that other people will be willing to do so too.
The high prices for art are due to demand from rich collectors, and the reason they are demanding art at the moment is because of its high prices.
Karl Marx wrote that value can mean two things. First, the obvious one – a jumper is valuable when you're cold, coffee is valuable when you're trying to write an essay, and so on. These are 'use values'.
The use value of a piece of art would be that it is beautiful or that it makes you think or brightens the room up, or something like that.
The other kind of value is what an object can be exchanged for – what it is worth in money. In which case, it doesn't matter whether what you're exchanging is a sculpture or half a ton of concrete, as long as it's worth the same amount of money.
Even though the first definition – whether something is useful to us or not – seems more logical, the important one under capitalism is the exchange value.
Everything exists to be sold and the humans involved are almost irrelevant.
The same is true for every commodity, but it is more obviously mad when applied to art. The millionaires who invest in art funds often don't even get to see what they've bought.
We wouldn't expect someone who invested in oil to have buckets of it in their front room. But because art is such a human, personal thing it seems wrong to treat it as just another commodity.
In the past, the rich viewed art slightly differently. Like today it was a status symbol, but there was also the idea of enjoying it for itself.
Being rich meant being able to own beautiful objects, rather than buying beautiful objects being a means of making yourself richer.
The German Marxist Ernst Fischer wrote, 'Pre-capitalist society had tended towards extravagance, carefree spending on a vast scale, lavish entertainments and the promotion of the arts. Capitalism meant sober calculation and the puritanical slide rule.'
The beautiful monuments commissioned by rulers of earlier civilisations were meant to show their power and wealth, and impress the rest of us.
Rulers today also have monuments dedicated to their wealth – skyscrapers.
Billions of pounds were spent building the Canary Wharf tower. They imported 10,000 square metres of marble for the lobby.
But unlike its equivalent in the past, the marble isn't carved into statues – there would be no point, because the statement being made is just 'look, we can afford tons of marble' and there would be no extra benefit in making it look beautiful.
The important thing to the capitalists is the money-making going on inside the buildings – which probably explains why they are so ugly.