Musée Rodin audio guide,
five stops, free.

He is larger than the photographs let on, and he is set high, so the first thing you meet is the underside of his feet. One hundred and eighty-nine centimetres of bronze on a stone block, set among the clipped box trees of a garden that runs between Les Invalides and the Eiffel Tower.

Read the pedestal before you look at the man. The letters are cut into the stone: The Thinker by Rodin, offered by public subscription to the people of Paris, 1906. This is not a cast the museum bought. Parisians paid for it themselves, it stood outside the Panthéon from 1906, and it only came here to the garden in 1922.

He was not born as this. In 1880 Rodin modelled him about seventy centimetres high as the crowning figure of The Gates of Hell, seated on the tympanum, and called him The Poet. He was Dante, leaning out over the edge to watch the circles of Hell while turning his own poem over in his head. So the figure you are looking at started as a man thinking about a book he was writing, surrounded by the people he had put in it.

The pose is borrowed twice over. Rodin had in mind Carpeaux's Ugolino from 1861, and behind that Michelangelo's seated Lorenzo de' Medici, carved between 1526 and 1531. Look at the arm. The right elbow is planted on the left thigh, which is not how anybody sits. That single wrong angle is what keeps the body from settling; every muscle in the back and shoulder is working to hold a pose that ought to be restful and is not.

He was exhibited on his own for the first time in 1888, while still staying in place on the Gates, and that is when he became a work in his own right. Enlarged in 1904 to the size in front of you, the colossal version turned out to be even more popular than the small one, and the man lost in thought whose body promises he could get up and do something about it became one of the most reproduced objects ever made. There are twenty-seven other known full-size bronzes of him around the world, not all of them cast under Rodin's eye, plus plasters, studies and dozens of posthumous casts at every scale.

One more is a grave marker. In the garden of Rodin's house at Meudon, another Thinker sits on the tomb of the sculptor and his wife.

Now turn around and find the other side of the garden. The dark rectangle against the pale wall is The Gates of Hell, and if you look at the top of the doorway you will see him again, a third of this size, exactly where he started.

From a distance it barely reads as a man. A tall wedge of bronze rising out of the grass, narrow at the foot and heavy at the shoulders, like something set upright rather than something standing. Then the head comes into focus, tipped back, and the whole thing turns into a person.

The Société des Gens de Lettres, the writers' society, commissioned a monument to Honoré de Balzac in 1891. Rodin took six years. He studied the writer's body and his head as two separate problems, and they went in opposite directions on him: the head moved away from a likeness and became a concentration of expressive features, while the body dissolved into the fluid surface of a dressing gown. What he ended up with in 1897 was an assemblage of the two.

The garment matters. Balzac really did write in a monk's habit, and Rodin dressed him in it and then took away everything else a nineteenth-century monument was supposed to carry. No armchair. No pen. No book. And, most provocatively, no hands at all. The gown closes over the arms and the figure ends. Look for the hands now and you will see how deliberately they are absent.

The full-size plaster went to the Salon on the Champ de Mars in 1898. The outrage was severe enough that the commission was cancelled, and Rodin took the plaster home to Meudon. He died in 1917 without ever seeing his Balzac in bronze. In 1935 the Alexis Rudier foundry cast this one for the museum's collections; four years later, on the second of July 1939, twenty-two years after the sculptor's death, a cast was finally set up in public, on the boulevard du Montparnasse where it meets the boulevard Raspail.

It is worth remembering what the museum hung beside it. The marble Kiss was put on show for the first time in that same year, 1898, as a companion piece to this Balzac; a marble everybody could love, standing next to a bronze nobody could. The Kiss is indoors and you will see it shortly. Balzac stayed out here.

It is now sometimes called the first truly modern sculpture, and it is easy to see why once you step back far enough that the detail drops out. The figure stops being a portrait and becomes a shape: one column of shadow and light, rising, with a head at the top of it and Les Invalides behind.

Colour, at last, and a great deal of it. After a morning of bronze and white marble you turn a corner on the first floor and there is a small man in a broad hat sitting in front of a wall of Japanese prints, painted in reds and yellows and greens that have not calmed down in a hundred and forty years.

His name was Julien-François Tanguy, he lived from 1825 to 1894, and he ran a paint supplies shop on the rue Clauzel. Painters called him Père Tanguy, Father Tanguy. He sold colours and canvas and he frequently took paintings in payment instead of money, which is why Émile Bernard said that walking into his shop in Montmartre was like visiting a museum. Van Gogh, who had come to Paris in March 1886 to live with his brother Theo, painted him three times. Tanguy never parted with this one.

Look at how he is placed. Strictly frontal, immobile, hands folded over his stomach, eyes level with yours. Van Gogh has posed a Montmartre shopkeeper the way a Japanese print poses a sage, and then papered the wall behind him with the prints from his own shop. Mount Fuji sits directly on top of the hat. Kabuki actors share the wall with cherry trees in flower. It is a portrait of a man and an inventory of his stock at the same time.

The painting itself is a young painter trying everything at once. Pure colours out of the tube, complementaries set against each other, every brushstroke left visible and deliberately placed, and no depth at all: the wall is as flat as the prints on it. Look at the coat, which is built out of short parallel strokes of blue and violet with no modelled shadow anywhere.

Which brings us to why a Van Gogh is hanging in a sculptor's house. Tanguy died in 1894 and his daughter sold the portrait to Auguste Rodin. Rodin was a serious collector of Japanese prints himself, with a holding comparable to Monet's or Van Gogh's, and he bought two other important works by Van Gogh besides this one. He talked about him often. In 1909 he called him an admirable demolisher of academic formulae who also had a genius for light.

Rodin's collecting went a long way past prints. In the last twenty years of his life he gathered Egyptian, Greek and Roman antiquities and then objects from the Far East, more than six thousand pieces by 1917, and he owned a Renoir and a Monet as well. This wall is part of what Rodin did with the money his sculpture made him.