Michelangelo and the mastery of drawing

One of the most common complaints made about today's artists is their apparent inability to draw. In matters of art, no question is more decisive, more majestically final, than: "But can he/she draw?" In a melodramatic hatchet job on Francis Bacon, Picasso biographer John Richardson recently claimed that Bacon's "graphic ineptitude" was his Achilles heel: "Tragically, he failed to teach himself to draw."

The pro-life-drawing movement is one of the most lasting legacies of the artistic Renaissance in Florence, for it was here that disegno (design or drawing) was enshrined as the source of all visual competence. The first art academy, founded in Florence in 1563 on the urging of Giorgio Vasari, was called the Accademia delle Arti del Disegno, and the curriculum centred on drawing of the live (and dead) model, and of approved artworks that would enable the aspiring artist to "correct" nature.

Michelangelo, a compulsive drawer whose most exquisite creations are the subject of a major exhibition at the Courtauld Institute Galleries, was being typically Florentine when he asserted that "Design, which by another name is called drawing . . . is the fount and body of painting and sculpture and architecture and of every other kind of painting and the root of all sciences." The preliminary drawings of artists are here seen as essential to the advancement of learning as the technical drawings made or commissioned by mathematicians, engineers, doctors and scientists.

The technical similarities between drawing and writing also added hugely to the former's allure and status. Florence had the highest literacy rates in Europe, and was justifiably proud that Dante, Petrarch and Boccaccio had established Tuscan as the pre-eminent Italian tongue. Artists wanted to share in that prestige, and establish the visual arts as a major liberal art. The two pre-eminent Tuscan draftsmen, Leonardo and Michelangelo, were also the most literate, and their sketches are interspersed with texts written in an elegant, calligraphic script. Michelangelo's drawings are interspersed with his own poems, and extracts from the Tuscan greats. Later collectors of drawings concurred: they bound them into books and kept them in their libraries. It is no accident that literature-loving England has the greatest collections of old master drawings, including those by Michelangelo.

Michelangelo furnishes us with the first and most famous "but can he draw?" anecdote. Vasari reports how they both visited Titian's temporary studio in Rome, and were confronted by a steamy nude painting of Danaë being inseminated by Jupiter in the guise of a shower of gold. Her pose derives from Michelangelo's sculpture Night in the Medici Chapel. Michelangelo, having praised Titian's colour and style, regretted that in Venice painters did not learn how to draw methodically from the start of their careers – what a great artist Titian would have been if only he knew how to draw!

Vasari smugly adds that if the artist "has not drawn a great deal and studied carefully selected ancient and modern works, he cannot by himself work well from memory or enhance what he copies from life". Here, priority is given to "intelligently" drawn line over "instinctively" painted colour, and this became an article of faith for all future art academies: the first director of the French Académie Royale, founded in 1648, asserted that, without drawing, painters would not rank any higher than colour grinders, the lackeys who prepared pigment.

Yet Michelangelo's attack on Venetian painting points to a serious flaw in the argument. One can compile an extremely impressive list of great (and mostly unliterary) artists who got by nicely without bothering unduly with drawing. They displayed not so much graphic ineptitude as indifference. Giorgione, Titian, Caravaggio, Hals, Velázquez and Vermeer seem to have painted directly on to the canvas, just incising or brushing in a few outlines. Indeed, drawing as a major artform has been in spasmodic but continuous decline since the 17th century: most drawings by great artists after about 1850, including Manet, Cézanne, Picasso and Matisse, are barely worth exhibiting and are of interest only to specialist scholars. Bacon represents the rule rather than the exception.

The aesthetic and intellectual highpoints of academic drawing are Michelangelo's so-called "presentation drawings", created in the early 1530s as pedagogic gifts for the young Roman aristocrat Tommaso de' Cavalieri, who was learning to draw. Using largely pagan subject matter, and made using red or black chalk, they tell moralising tales, mostly about men and love. They are Michelangelo's most highly finished and elaborate drawings, and as technical and imaginative feats have never been surpassed. The Courtauld exhibition, expertly curated by Stephanie Buck and with a substantial catalogue, is the most important ever devoted to them.

The "divine" artist, then in his late 50s, had fallen in love with the teenage Cavalieri, who was famously beautiful, refined and (for his age) cultured. Michelangelo's feelings were reciprocated, and so he sent rapturous love letters and poems (several manuscripts are included), and drawings which his young protégé copied and commented on. It is the greatest correspondence course ever conducted. Drawing had become a respectable pastime for Italian aristocrats. In Castiglione's famous conduct book The Courtier (1528), drawing lessons are recommended – drawing enables us to appreciate the beauty and proportions of living bodies and the whole of the natural world, as well as to make maps for warfare.

Although Michelangelo was evidently homosexual, it seems unlikely his relationship with Cavalieri was ever consummated. The evidence suggests he was for the most part celibate, and in 1529 he had held high rank in the short-lived republican government of Florence, which was ardently anti-sodomite. The affair was conducted openly, with the drawings and poems being shown immediately to friends and to members of the papal court, and to artists who copied the drawings. Indeed, it was not uncommon for an aristocratic youth to have an older man as a mentor and even "platonic lover" – a term that had been coined by the Florentine philosopher Marsilio Ficino. In Ficino's Commentary on Plato's Symposium on Love (1474), written for Michelangelo's first patron, Lorenzo de' Medici, the relationship between an older man and a boy had been given the most exalted status:

"Among lovers beauty is exchanged for beauty. A man enjoys the beauty of a beloved youth with his eyes. The youth enjoys the beauty of the man with his Intellect. And he who is beautiful in body only, by this association becomes beautiful also in soul. He who is only beautiful in soul fills his bodily eyes with the beauty of the boy's body. Truly this is a wonderful exchange. Virtuous, useful, and pleasant to both."

The man receives supreme sight-food; the boy, supreme soul-food.

Ficino, a famous teacher, believed that the teacher-pupil relationship should always be based on mutual love. Turning to the visual arts, he insisted that whoever loves works of art and the people for whom they are made "executes [them] diligently and completes them exactly". This is the formal framework within which Michelangelo and Cavalieri's relationship is conducted. Ficino insisted that such relationships should not have a physical component (look and listen but don't touch or lust). Yet Michelangelo's poems, letters and drawings leave us in no doubt that he was often straining at the leash. In one poem, Michelangelo dreams of a day when he can hold Cavalieri for ever in his "unworthy yet ready" arms; then, more masochistically, he wishes his own skin could be flayed and made into a gown and shoes to be worn by his beloved. He wouldn't be allowed to teach this way today.

At the Courtauld, we can see all three versions of The Fall of Phaeton, a story highlighting the dangers of youthful hubris. The first drawing carries a note along the bottom whose modesty is amazing when we consider Michelangelo was at the height of his powers and prestige: "Messer Tommaso, if this sketch does not please you, say so to Urbino [Michelangelo's servant] in time for me to do another tomorrow evening, as I promised you; and if it pleases you and you wish me to finish it, send it back to me."

It seems the first version didn't get Cavalieri's complete approval (and Michelangelo was probably already dissatisfied), because the final version is more tightly structured and elongated. Phaeton was granted a single wish by his father Apollo, and chose to drive the chariot of the sun. When Phaeton lost control, Jupiter struck him with a thunderbolt to save the earth from incineration. Michelangelo made a vertical triptych shaped like an isosceles triangle, with Jupiter astride an eagle at the top, Phaeton tumbling spectacularly from his horse-drawn chariot in the middle, and his weeping sisters being transformed into trees at the bottom. All the figures are nude, and the whole intricate mise en scène presages Christ's casting down of the damned in the Last Judgment (1534-41).

The Courtauld is staging this exhibition both because the British Museum bizarrely excluded the Cavalieri drawings from its Michelangelo exhibition in 2006, and because the Courtauld owns one of the most compelling, known as The Dream. Its focal point is a lithe male nude perched on an open-fronted box. He leans back against a large sphere, signifying the world, which he clasps. Inside the box are a selection of different theatrical masks, suggesting deceptive and illusory pleasures. In the hazily sketched background is a heaving semi-circle of interlocking figures representing six of the seven deadly sins – Gluttony, Lechery, Avarice, Wrath, Envy and Sloth. The central male nude must signify Pride, yet he is being awoken from his deluded state by a trumpet-blast from an angelic winged boy, who has swooped down from the sky.

It's ostensibly a picture concerned with spiritual rebirth, but this reading is qualified by the explicitness and ingenuity with which Michelangelo has depicted the sinners – above all the Lustful, who spring up from the curve made by the dreamer's torso and thigh. There are two heterosexual couples, one nude and in flagrante, with the man's penis exposed; the other semi-clad and kissing (with the woman dominant). Michelangelo also depicted a huge erect phallus held by a hand emerging from clouds, and a graffiti-style penis. A naked man seen from behind, beneath the unattached members, may allude to homosexuality.

The penises were mostly erased by a subsequent owner of the drawing, and we know about them from a print made after the drawing, which is shown nearby. Here, too, Michelangelo seems to be straining at the leash, revelling in the power of the penis just as he denounces it. Like St Augustine in the Confessions, he may have muttered to himself: "Grant me chastity and continence, Oh Lord, but please, not yet."

The term "presentation drawing" – a finished drawing made as a gift – was devised by the great Michelangelo scholar Johannes Wilde (1891-1970), who taught at the Courtauld and was directly responsible for its acquisition of the Seilern collection, which included The Dream. There have since been many contrived attempts to trace a lineage for Michelangelo's presentation drawings in earlier Renaissance art, but beyond a few portrait heads or modest figure studies, there are no directly comparable drawings, and certainly not enough to suggest the existence of a genre.

I believe the only real precursors and indeed the inspiration for Michelangelo's drawings for Cavalieri were the enigmatic mythological prints made by artists such as Mantegna, Marcantonio Raimondi and especially Dürer, which were often given away as gifts. In terms of their range of mark-making and finesse, Michelangelo's presentation drawings for Cavalieri are the first drawings to surpass Dürer's prints, which were widely admired in Italy. In the past, many scholars claimed that Michelangelo despised this "minor" reproductive artform, but he must have been thinking a great deal about prints because he planned to publish a (never-completed) illustrated treatise on movements and gestures. The exhibition runs with this idea, and gives a starring role to Dürer and print-making.

The most risqué section of The Dream must have been informed by a very different kind of print, because in the 1520s the first illustrated pornography books were published – Marcantonio's I Modi (The Positions) with each of the 16 images accompanied by an obscene sonnet by Pietro Aretino, and Perino del Vaga's less explicit Loves of the Gods. The pope banned I Modi "since some of these sheets were found in places where they were least expected" (Vasari), and it seems inconceivable that Cavalieri (who collected prints) had not seen them, because otherwise Michelangelo's mini-Modi would have been too shocking.

The painstaking mark-making of the Cavalieri drawings is also found in a series of images of Christ made for the devout aristocrat Vittoria Colonna in the late 1530s, which she studied with a magnifying glass. But after that, Michelangelo turns his back on precision, perfection, beauty, control. In a parallel display, the Courtauld is showing its black chalk drawing Christ on the Cross (c1555-60), made when Michelangelo was in his 80s. It is defiantly anti-academic. Each line is drawn and then redrawn, so that Christ's slumped body becomes a quivering, boneless mirage, flayed and frayed, a crumpled cloak that a tramp might wear. Fra Angelico supposedly wept every time he painted a crucifixion, and Michelangelo's tremulous technique implies that he drew with and through tears. Michelangelo's younger self would surely have said: if only he had learned how to draw!

Michelangelo's Dream is at the Courtauld Gallery, London WC2 (020 7848 2526) until 16 May.