Three

At Tate Britain there is a room of sketches and studies, 'odds and sods', by Turner.

I spent a lot of time in there, and much time in front of this painting. The room is dimly lit, to protect the watercolours, but I think it allows the pictures to hover, and hypnotize.

Joseph Mallord William Turner. An Avenue of Trees ?c.1822

At first glance it looks plain and flat. Three cricket stump verticals and a hanging pink stripe. But after a while it pulled me in. Heavy with atmosphere, a smoky damp evening stillness, three trees in a clearing, and that great suck of depth through the avenue to the right.

And again the rich colour, the brushwork, the leaving nearly everything out. Almost abstract, only the essentials.

It would have looked terrible with two trees, or with four. One could work, perhaps five.

But three seems to be the magic number.