Tricks of the light: Weird visions in art

Could it be magic? Would it be better if it were? For most of the 20th century, modern art was considered a secular thing. Modern man didn't believe in God and spirits. Modern art didn't either. But recently the story has been turned around. More and more, modernism has been linked to the supernatural – to myth, ritual, visions, the occult, all that.

Last year, Traces of the Sacred appeared at the Pompidou Centre. It implicated practically every famous modern artist in the otherworldly, and introduced some lesser-known weirdos for good measure. Now we have a domestic version. The Dark Monarch: Magic and Modernity in British Art opens next weekend at Tate St Ives.

The title makes a local connection. The Dark Monarch is a novel by Sven Berlin, artist and writer, member of the St Ives artistic colony. Written in 1962, it was a roman à clef too libellous to be published at the time. I've never read it, and I'm sure I never will. But that phrase is certainly spellbinding.

St Ives is famous for its quality of light. And the Tate there normally has clear white spaces. But the powers of darkness have fallen on it now. The gallery's wide glass front is tinted over. The rooms are painted in shady hues. The works are gathered densely, more like a collection than an exhibition. The entrance piece is The Child's Dream, a sweet little woolly unicorn, pickled by Damien Hirst. Ahead wait standing stones and haunted woods and mumbo jumbo. But already the show is conjuring up a faery, spooky air.

In this context, familiar and austere works of modern art are given a new, weird emphasis. Take two Barbara Hepworth sculptures: Two Figures (Menhirs) and Group of Three Magic Stones. What would normally have passed just as poetic titles here become something more. What are they suggesting? That there was a bit of a pagan in Dame Barbara? That these shiny pieces hold ancient power?

The trick continues. Classic pieces of British modernism are subjected to a series of double-takes. You thought it was plain art. It acquires darker depths. Henry Moore's stone Mask – might it actually have a ritual function? Or Graham Sutherland's Horned Forms: in its half-abstraction, might there lurk the forces of an animistic nature? Or Paul Nash's Mansions of the Dead: this surely is like some spiritualist vision of the hereafter. And Nash could have provided much more. Almost all his mature works have an overt visionary edge.

But I don't think any of these artists actually held any pagan or spiritualist convictions. They simply knew (say) the standing stones of Cornwall and saw where their art could draw strength. And though this is a show that tends to blur differences, compacting the genuinely occult with the charmingly spooky, there are obviously distinctions to be made.

Take the now almost forgotten Cecil Collins (he had a retrospective at the Tate only 20 years ago). He created a world of sun-faced angels and holy fools. It came out of surrealism and developed into a kind of Blake/Tarot imagery. The point is, it's very sincere, the art of a believer. What exactly Collins believed in, I'm not quite sure. Perhaps it could only be expressed in his pictures.

Or if Collins is getting obscure, how about another former British Surrealist, Ithell Colquhoun. Like many Surrealists, she was expelled from the movement. And like many Surrealists she had occultist and magical tendencies, to which she then devoted herself even more seriously. Her visual works are often weak. But perhaps that's the mark of the true believer.

Meanwhile, in the contemporary side of the show – but it isn't separated out, all the works are interleaved non-chronologically, so as to set up odd connections – the mood is a kind of faux-seriousness. These artists are certainly not believers, though they know their subject. They're attracted to occultism for its pseudo-methodical nuttiness, the way it's a kind of parody of science. They can pick it up, and play with it further.

It's hard to describe the cod-magic gadgetry devised by Cerith Wyn-Evans, Adam Chodzko or Mark Titchner. But their titles communicate the general spirit: Anthropomorphic Portrait by Sulwyn Evans, Wilhelm Reich in Black Ash Hell. Jokey is the word.

The only artist to make something in this vein worth looking at is the sculptor Eva Rothschild. In High Times, cascades of leather strips hang inexplicably in mid-air. A new age aesthetic meets a trick of very homemade conjuring. It's a proper piece of sculpture. And it's not jokey, it's funny.

But as I say, things are mixed up here. The believing, the non-believing and the faux believing are exhibited cheek by jowl, and the effect is to cast a spell of confusion over the whole show. Of course, we all like the supernatural, and the more the merrier. It's fun to see the solemn forms of Henry Moore recast as Hammer horror props. For ages we've heard how modern art was inspired by tribal art. So let's take "primitivism" literally.

Yes, let's go further, and imagine that all those unnoticed public sculptures suddenly become conspicuous, as, week by week, horrifically, at the dead of night, they are used as altars for human sacrifice. The police are baffled. Art historians are called in. Should we have foreseen it, when, in the 1950s, these apparently benign lumps of art were plonked all over the country? What sinister cult is making use of them? Was Moore himself a member? It's a good beginning for a story.

It makes my point as well, too. Of course Henry Moore isn't really voodoo. And when it comes to the occult etc, one must decide what one believes: yes or no. The Dark Monarch has collected a marvellous variety of evidence, but it blurs where it could distinguish. It's not alone. There are writers today, like Peter Ackroyd or Marina Warner, who love to invoke the supernatural, without really ever making it quite clear whether for them it's a real realm or a handy metaphor.

They're like those soft theologians who say that God is only a name for our sense of ultimate meaningfulness. For these soft magi the supernatural is only a name for our sense of endless possibility, a way out from the grey rational world, imbuing life with depth and romance. They don't really credit spirits, powers, demons. They couldn't cast a spell to save their lives. They want to borrow the glamour and prestige of magic but they don't reckon at all with what magic, if it existed, would imply.

So here's a telling tale from the history of British magic, not from art but politics. Perhaps you remember, back in the 1980s, when unemployment was rising. Margaret Thatcher said that, if only she had a magic wand, she would get rid of it at a stroke. Her point was, she didn't wish it; sadly, it was an economic necessity.

But think: never mind the unemployed, if Margaret Thatcher had really wielded a magic wand, what else would she have done with it? It beggars belief. If people generally had magic wands, the world would be a madhouse. Let fantasy stay fantasy. The resistance of reality to human wishes, strange to say, is a blessing beyond imagining. Art, please note.

The Dark Monarch: Magic and Modernity in British Art, Tate St Ives (01736 796226; www.tate.org.uk/stives) Sat to 10 January