At the press launch of the Royal Academy exhibition of Poussin paintings, a member of the audience asked why no mention had been made of Anthony Blunt. Richard Verdi, chief organiser of the show, replied that current scholarship was "neither anti nor pro-Blunt, simply post". His statement was, however, somewhat contradicted by National Gallery director Neil MacGregor. Blunt's research has remained indispensable for all Poussin scholars, according to MacGregor: "Everyone who has ever worked on Poussin is a student of Blunt. If there are some disagreements on attribution or dating, this is simply the readjustment of an enormous edifice but the edifice itself is not being challenged."

Blunt's Poussin studies and writings spanned the art historian's life from the early 1920s until his death in 1983. The Louvre's director, Pierre Rosenberg, stated at the Academy opening that "nothing can be done in art history without an international outlook", and this helps to explain the quality of Blunt's contribution. In his early publications during the 1940s and 1950s on artistic theory in Italy, on the 16th-century architect Francois Mansart, and on French Renaissance and Baroque architecture, one of the first great British art historians (as opposed to connoisseur) built up an astounding knowledge of Poussin's epoch.

Every aspect of Blunt's book is closely reasoned, using a vast array of historical and visual documentation. Set in his historical context, Poussin comes to life as a constantly developing personality, resistant to any simplistic explanation. One thing is certain: Poussin's themes were not simply the reflection of the artist's personal fortunes, or a reflex action to the buffeting of fate. On the contrary, though a practising Stoic, the painter exercised a great deal of control over his own life, beginning with his early decision to travel south to Rome, and continuing later in the way he worked on his own, determined that he should decide what and how he painted. Blunt writes: "Poussin was indeed the tortoise of painting, and he was proud of the fact." The artist's painstaking struggle to deepen his knowledge of anatomy, geometry and perspective and drawing paid off: by 1630 he had made some notable masterpieces, including "The Inspiration of the Epic Poet".

He was summoned back to Paris by the French king in 1640, and reluctantly left Rome. He found the intellectual atmosphere in Italy freer and more congenial than that of his native France. He returned to Rome late in 1642, never to leave again.

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Although his first public commission for the Barberini papal family was a failure, Poussin built up a network of patrons who granted him a treasured artistic liberty. These included Cardinal Giulio Rospigliosi, later Pope Clement IX, and Cassiano del Pozzo, a lawyer who became secretary to Cardinal Francesco Barberini. Pozzo offered Poussin a haven of intellectual stimulation, ranging from the natural sciences to a profound study of the world of antiquity, which, as Blunt writes, was "imaginative rather than pedantic".

The artist's choice of subject matter set him apart. He returned time and again to certain classical myths: Apollo, Bacchus, Pan, Adonis, Priapus, Venus, Diana, Flora, Hyacinth and Narcissus people his canvases. Religious subjects from the Old and New Testaments are just as common in Poussin's oeuvre, and again the artist's concentration on particular themes is meticulously set out and analysed.

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Blunt quotes from Poussin's first biographer, Giovanni Bellori, to show how the painter applied his philosophy to the practical conduct of his life "in the most exact manner". His range of intellectual influences was not confined to the world of Rome. He maintained a group of French patrons for many years. Before leaving Paris in 1642, Poussin attended a dinner with outstanding French men of learning, including the philosopher Pierre Gassendi, a keen supporter of the Copernican system and admirer of Galileo. Gassendi and his co-thinkers were known as libertins, rationalist humanists "who saw in the teachings of ancient philosophy a moral code on which to base their lives". Blunt explains how these 17th-century thinkers "were animated by a hatred of superstition and mocked the credulity with which the ignorant accepted stories of miracles, sorcery, witchcraft and so on. They attacked and satirised the corruption of the Church, particularly as they saw it in the court of Rome and to some extent in the higher clergy in France . . . their inspiration was the philosophy of the ancients."

Poussin brought together the best of several worlds: the superb painting techniques of the Italians, the freedom of working for a select group of patrons, the intellectual ferment of an independent group of European thinkers. He tamed the wildly extravagant style of the Roman Catholic Baroque into a passionate but controlled style.

He differs from such grandly rhetorical baroque contemporaries as Bernini and Rubens in that his "messages" require careful unravelling. He explained this to his friend and patron, Paul Freart de Chantelou: "Things of perfection must not be looked at in a hurry, but with time, judgement and understanding. Judging them requires the same process as making them." But it is not simply the incorporation of mythical beings into a landscape that gives Poussin's work, especially his late landscapes, such beauty and gravitas. They are the visual expression of a dynamic new philosophy. The Stoic ideas shared by Poussin's circle are, Blunt writes, "curiously in accordance with modern ideas in that they seek the origins of the myths in the primitive feelings of man about nature, and his desire to embody her forces in some semi-human form which he can hope to comprehend and so hope to control". His book weaves these concepts into a detailed analysis of the structure and content of the paintings themselves. Finally, in an inspired mental leap forward, Blunt reveals the continuity between Poussin and great modernists such as Cezanne and Picasso.

The Pallas Athene reissue contains an invaluable set of indexes, bibliographies and a complete set of 265 black and white plates of the artist's oeuvre.

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Martin Clayton's Poussin: Works on Paper incorporates the extensive research on the artist carried out in the 50 years since Blunt completed his catalogue of the French drawings at Windsor Castle. The book reproduces in colour all the drawings from the Queen's collection on show at the Dulwich Picture Gallery.

Poussin's drawings, even more than his paintings, reveal that he saw the human body as a vehicle for emotion and thought. It is this symbolic content, not a spontaneity of vision, that gives them pathos.

Part of the London celebration of Poussin includes a special display of "A Dance to the Music of Time" at the Wallace Collection. The accompanying book is an exceptionally beautiful and useful examination of this enigmatic painting and the patron who inspired it.

For a more detailed appreciation of Poussin's compositions, his use of colour and paint, Rosenberg and Damian's book is invaluable and accessible. The two French art historians show how boldly sensuous Poussin was in his use of paint and colour, by selecting 40 of his works and using enlargements and comparisons to help the non-expert.

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Corinna Gilbert is an art critic and art historian who studied at the Courtauld Institute when Anthony Blunt was the director.