Reynolds and Gainsborough, divided by technique and temperament, were united in their discontent with the narrow scope of 18th-century English portraiture. Andrew Gra-ham-Dixon detects a secret spirit of rebelliousness in two paintings on show at the Queen's Gallery, London
''Damn gentlemen,'' he once wrote to a friend. ''There is not such a set of enemies to a real artist in the world as they are, if not kept at a proper distance. They think (and so may you for a while) that they reward your merit by their company and notice; but I who blow away all the chaff and by God in their eyes too if they don't stand clear, know that they have but one part looking at, and that is their purse . . .'' Few society portrait painters have been as lacking in servility as Thomas Gainsborough.
His portrait of Henry, Duke of Cumberland with the Duchess of Cumberland and Lady Elizabeth Luttrell, currently on view in ''Gainsborough and Reynolds'', a small but nutritious exhibition at the Queen's Gallery, is among other things a masterpiece of disguised impertinence. Three aloof aristocrats and a panting lapdog find themselves in a bower of bliss of the artist's devising, a sylvan twilit glade containing an urn on a plinth. They are surrounded by tall and fantastical trees like madly outsize sprigs of parsley, and overhung by foliage painted so quickly and fluidly that it looks more liquid than solid. It forms green cascades and waterfalls which tumble down from a gold and blue evening sky where a pair of tiny white birds, each formed from just two brushtrokes, hover. But all is not entirely harmonious in Gainsborough's earthly paradise. The people who inhabit it strike a false note, as if they have accidentally wandered into the wrong sort of picture. There is something vulgar and crass about them, in the circumstances: they look like too-courtly courtiers posturing in the forest of Arden.
The portrait is a small but caustic allegory on the theme of nature versus culture. The Duke, a notoriously dissolute and vain man, has dressed up to the nines, even though he is only out for a walk in the country. He is the epitome of effete and preening self-satisfaction, in his gold braid and his star and garter. His left foot is turned out in a fashion which recalls Dr Johnson's famous remark about Lord Chesterfield - ''the manners of a dancing master, and the morals of a whore'' - and the garter beneath his knee has been arranged mischievously by the painter so that the only visible part of its inscription, ''Honi soit qui mal y pense'', is the word ''mal''. The Duchess, taller than her husband and older than him - their marriage was much disapproved of, and she was considered to have been something of a gold-digger - is a proud and cold-faced woman in ice-blue finery. Her younger sister, Lady Luttrell, languishes beneath a tree in what might be charitably interpreted as a fashionable late-18th-century attitude of melancholic reverie, but the more you look at her the more bitter and worldly she seems: a green and jealous figure, loitering at the margins of her big sister's world and envying her her good fortune. She lost much of her money gambling and eventually died, in obscurity, in Germany.
Gainsborough's portrait is a wonderfully revealing picture and not only because of what it reveals about the artist's attitude to a small and particular group of English aristocrats. It is a painting filled with a new and distinctively English 18th-century spirit of artistic dissent: a picture in which can be sensed the brewing dis-content of a whole generation of English artists, profoundly dissatisfied with the limited scope of the limited subjects which their patrons were prepared to commission from them.
Gainsborough, in his letters, never tired of complaining about the restricted tastes of the English gentry, which forced him to earn his living as a ''phizmonger'', a painter of the faces of the rich. One of the ways in which he responded was to paint portraits that were more than portraits and which now seem almost indifferent to the mere and mundane capturing of a likeness. Gainsborough's great skill was to invent a kind of portrait painting that was so far removed from the portrait painting of the earlier 18th-century that it allowed him the freedom to exercise his imagination.
In the end he did not paint people, but Gainsboroughs, and this is especially noticeable in his female portraits: his women became dryads, unreally vast and gorgeously dressed spirits of nature, more like feathered creatures than flesh-and-blood human beings, inhabiting imaginary arcadias of paint. What is unusual about his portrait of the Duke and Duchess of Cumberland is its daring note of satire: its bold suggestion that these people are not good enough to inhabit the pastoral fantasy that was Gainsborough's invented world. But all Gainsborough's later portraits are, to a greater or a lesser extent, pictures that go against or seek to defy the limitations of society portraiture: they proclaim, first and foremost, the genius and imagination of the artist, not the virtue or beauty of his sitters.
SIR JOSHUA Reynolds was a very different kind of artist: slower, more ponderous, more self-conscious and much more deliberately Old Masterly in the many allusive styles of his painting. The two painters never got on terribly well together, separated for most of their lives by a spirit of rivalry. Yet this exhibition suggests that, despite their extremely different talents and temperaments, they were both responding to the same cultural predicament - and that both were inspired by a surprisingly similar form of discontent with the status quo.
Reynolds painted Frederick William Ernest, Count of Schaumberg-Lippe as a military hero, worlds away from the arcadian fantasy of Gainsborough. Placed, not in a quiet glade but on the large and noisy stage of History, he stands between a smoking cannon and a military banner while his black page restrains his fiery and romantic warhorse: a stallion by Titian out of Velazquez. Heat and dust and battlesmoke coil vaporously across the canvas. This is not a pastoral but an epic: an image of one man's imperturbable sang-froid in the heat of battle but also an image of war in the abstract, glorified and aggrandised by an artist's imagination, although it has to be said that the picture is not entirely effective, partly because Reynolds was not as felicitous an artist as he would have liked to be (the echoes of other and greater artists always present in his art rarely work in his favour) and partly because the sallow-faced and balding general who was his sitter makes for a slightly unconvincing hero.
However different it may look, Reynolds' portrait does have something vital in common with Gainsbor-ough's. It is a picture that speaks of the artist's implicit dissatisfaction with the narrowness of conventional 18th-century English portraiture. It is a portrait that wants to be more than a portrait, that aspires to the condition of a grand narrative painting just as Gainsborough's portraits so often, themselves, aspire to the condition of pastoral mythologies.
THE EXHIBITION also includes pictures which Reynolds and Gainsborough painted, not for their patrons, but for themselves. Reynolds contributes the less than convincing Cymon and Iphigenia, a history painting that draws its subject from Boccaccio: a goatherd comes across a nude and beautiful young woman in a dark forest glade and gawps at her, in this distant pastiche of the encounter between Cupid and Psyche painted for Charles I by Van Dyck. Gainsborough's one mythological painting, his late unfinished Diana and Actaeon, by contrast, is a great and extraordinary painting which seems to look forward in time rather than back, a loose and fluid image of nude women under trees and by a pool that anticipates the bathers of Cezanne and Matisse. Again, although their themes and approaches are quite distinct, Reynolds and Gainsborough have something in common: an ambition and an imagination that run against the grain of pure portraiture.
The overt theme of this exhibition - its subtitle is ''Contrasts in Royal Patronage'' - is the use to which the royal family put the differing talents of Reynolds and Gainsborough. The two Georges, George III and George IV, inherited the literal-mindedness and some of the philistinism of their Hanoverian forebears - ''I hate bainting and boetry,'' George I used to announce in his thick German accent - and as a result they always preferred the portraits of Gainsborough, which they considered to be natural and unassuming, to the more learned and elaborate and flightily Baroque portraits of Reynolds.
But what the show most memorably reveals is the secret similarity between two of the founding fathers of a truly English form of painting. Reynolds said that he would have liked to be Michelangelo and Gainsborough painted as if he would have liked to be Watteau. What united them was their desire to be other than they were, and their subtle defiance of a society whose tastes they found restrictively narrow. In 1788, Gainsborough, on his deathbed, sent for Reynolds and they were at last reconciled: perhaps recognising, in the end, that they had both fought the same battle.