Exhibitions: The drawings he didn't want you to see

Francis Bacon: Works on Paper and Paintings Tate Gallery, London

For Francis Bacon, only the very best or the very worst in life would do. Whether he was enjoying a glass of the finest champagne or a beating from a street tough, in his art as in his life there seemed to be no middle ground. Of course, he did not always live at life's extremes, but he made it appear as if he did, and his circle of friends, lovers, collectors and critics adored him for it.

Initially inspired to take up painting by seeing the work of Picasso when he was living in Paris between 1926-28, Bacon did nothing so mundane as go to art school. Rather, back in London in 1929 aged 20, he set up a studio and began to work. Sixteen years later the triptych Three Figures at the Base of the Crucifixion was hailed by the critic John Russell as "a watershed in British painting."

This was a remarkable achievement, made all the more so by Bacon's insistence - and its acceptance by those who talked to and wrote about him - that he never made any preparatory studies for his large oil paintings, but worked straight on to the canvas. This impression of work successfully achieved without any form of intermediate struggle was reinforced by his habit of destroying any paintings which did not satisfy him.

Bacon readily acknowledged the inspiration he found in photographs, including Eadweard Muybridge's studies of the figure in motion, and film stills such as the famous Odessa Steps sequence from Battleship Potemkin. The working process by which such sources became his final, painted images might perhaps have been revealed had David Sylvester, during any of the interviews he conducted with the artist between 1962 and 1984, ever mentioned the series of small pencil sketches he had noticed in the endpaper of Bacon's paperback edition of the works of T S Eliot. But the foremost Bacon authority "courteously refrained" from asking about them while their creator sat before him denying that he ever did any drawing other than directly on to his canvases.

The existence of other drawings should be a surprise to no one except those who believe artists to be magicians rather than makers. In this sense, Bacon obliged his audience. He too believed in the magic of painting, its ability to tell a lie that revealed a greater truth. In pursuit of such profundity, what did it matter if a few drawings were destroyed along the way? Those now to be seen at the Tate seem to have been an unusual exception, given to his friends Peter Pollock and Paul Danquah, in whose Battersea flat he lived and worked from 1955 to 1961. Four other drawings were a gift from the artist to the poet Stephen Spender, who had written three articles about him in 1961-62. That he would give drawings as gifts suggests that he did indeed value them, if not as works of art in themselves then certainly as something sufficiently personal to stand as tokens of the esteem in which he held their recipients.

The drawings are perhaps best understood not as any form of academic studies, but as notes, differing little from the written notes which sometimes accompany them. In a sprawling, open hand, they listed possible subjects for compositions in general or, in one case, specific components of a particular painting, which might well have resembled Seated Figure (1961), one of the selected paintings hung in the adjacent gallery.

Anyone who thinks that so tightly balanced and complex a composition was achieved entirely without premeditation is simply not seeing what is on the canvas before them. For, despite his lack of training in figure drawing, Bacon was certainly skilled in organising the pictorial space of his paintings. In his early years, Bacon worked briefly as an interior designer, and his compositions always suggest an ease with the arrangement of things and planes in space. In Seated Figure, a few spare, thin black lines set up a kind of spatial box. At the very centre of this, the true raison d'etre of the picture is addressed, that "pool of flesh" identified in a pencil note in the margin of his sketch Two Owls. In paint Bacon does seem to work by instinct, scraping and dragging and spattering until the mess of blobs and smears at the epicentre of the canvas resolves into a recognisable, undeniable, human face.

It could be said that Bacon was not dissembling when he denied that he made drawings, for he had no interest at all in producing drawings as finished products. The pages from his sketchbook show figures sitting, falling, lying and twisting, forming a vocabulary of figures in motion.

Some of the drawings certainly have that familiar Baconian power to send a shudder of spontaneous revulsion through the spectator. The extraordinary violence of those blobs of pigment heaped up on sheets of grubby, oil- smeared paper, is startling, their unruly life controlled within a cage of swift pencil or ball-point pen strokes. But the magnificence of Bacon's paintings is in no way undermined, as he may have feared, by seeing these few traces of what may have been their genesis. In fact it is reassuring to see how consistent Bacon's thinking process was. "Great art is deeply ordered," he observed, and his was. The links between the found images which intrigued him enough to be noted down in these quick sketches and those in his finished canvases seem unambiguous. It is perhaps not surprising that Bacon's belief in order was overlooked by those who experienced the dazzling disorder of his working conditions - the famous paint-spattered studio, knee deep in drifts of torn books and magazines, photographs and papers.

Looking closely at, say, the study after the life mask of William Blake, the image appears to materialise on the canvas from within a welter of random marks and splatters which somehow become form. Ultimately, it is the product not of any particular process but of the artist's will to somehow, anyhow, pin down the soul within that "pool of flesh". For Bacon, nothing else - especially the niceties of academic drawing - mattered.

Francis Bacon: Tate, SW1 (0171 887 8000), to 2 May.