On 7 March 1932 Oskar Reinhart – two days in to a ten-day trip to London from his home in Winterthur, Switzerland – had lunch with his fellow art collector Samuel Courtauld. Reinhart admired some of the paintings in Courtauld’s collection. He thought Van Gogh’s Self-Portrait with Bandaged Ear an important work. Cézanne’s Man with Pipe he liked even more: ‘first rate’, he wrote of it in his diary, ‘one of the most beautiful Cézanne’s I have ever seen’.

That, as far as we know, is the sum of their relationship, but in other respects, the two were deeply connected. They were near-contemporaries, born nine years apart – Courtauld in 1876, Reinhart in 1885. Both men inherited deep fortunes from their family businesses: Courtauld’s in textiles, Reinhart’s in shipping and insurance. Both amassed great collections of Impressionist art, albeit with slightly different emphases: Courtauld’s collection looks forward to post-Impressionism; Reinhart’s looks back to the early 19th century. Both took advantage of the glut of great works that came on to the market as some private fortunes declined in the aftermath of the First World War.

Perhaps more importantly, both believed their collecting to be almost a social duty: Courtauld established the Courtauld Gallery to display his art; on his death Reinhart left his villa, Am Römerholz in Winterthur, to the Confederation of Switzerland to house his. It is fitting, then, that – while Am Römerholz is closed for renovation, 25 of the masterpieces that Reinhart acquired should find their way to the Courtauld in London for Goya to Impressionism, a superb temporary exhibition that runs until 26 May 2025. That they have never been exhibited together outside Switzerland might be reason enough to visit; but the way they sit in dialogue with the permanent collection in the Courtauld’s main rooms nearby surely offers a unique opportunity that will not arise again.

If the sense of conversation and colloquy reverberates powerfully through the exhibition, we are reminded just how provocative much of this art was in its day by the very first work on display. Goya’s highly charged Still Life with Three Salmon Steaks was painted during the Peninsular War of 1807-14, which brought Spain, together with its Portuguese and British allies, into conflict with Napoleon. The steaks rest, crisply lit, on a grey stone or metal surface against a black background. It has sometimes been seen as safely neutral, apolitical work – alongside other still lives he painted in those years. But it has a quality of blankness that is almost aggressive in its refusal to reveal itself, and paradoxically that makes it feel the most modern piece here.

All but seven of the paintings here come from the three decades or so after 1870 and track the astonishing speed of artistic change. There are six paintings by Cézanne among the 25 on display; like Courtauld, Reinhart thought him the leading figure among the Impressionists. Those six works span 40 years, and the transformation that his art undergoes in those years is remarkable. The first, from 1866, is a portrait of his maternal uncle Dominique Aubert, whom he painted ten times or so; commissions were thin on the ground. It’s a muted, almost sombre portrait: Aubert’s clothing is dark against a darker background; the light falls on his face, which rests – a touch resignedly – on his balled-up fist.

That face is magnificent, the paint applied thickly with a palette knife so that the impasto’s rough, blocky texture seems encrusted on the canvas. It is like seeing a portrait beneath coarse uneven glass: you can’t not see the paint even as you see through it to Aubert’s luminous features beneath. It’s the painting here that most insists on the physicality of its medium. Cézanne’s last work in the show, by contrast, is almost ethereal. It’s one of his innumerable views of Mont Sainte Victoire near his home in Aix-en-Provence and dates to the last years of his life; he died shortly after being caught in a storm while working on another.

This iteration is a watercolour: the mountain’s outline is sketched in pencil; in the foreground, pale splashes of blue, green, red and yellow suggest the indistinct forms of trees and houses, paler yet are the blues of the mountain and the sky beyond. Throughout, but particularly the margins, it fades into absence as if the whole work is floating on the surface of the paper. (The Courtauld has a strikingly different version of Mont Sainte Victoire, steeped in Provençale summer heat, in its permanent collection.)

Cézanne copied the palette-knife technique from Gustave Courbet, who used it extensively in a series of paintings he made of a great wave beneath a brooding Normandy sky. It’s hard to beat Cézanne’s own description of the power of these pieces: the tide ‘appears to come from out the depth of ages, it hits you in the stomach’, he wrote. ‘You have to step back. The entire room feels the spray.’ That’s certainly the effect of the example in Reinhart’s collection, executed in 1870. Much of its intensity surely comes from the fact that Courbet denies you the comfort of the shore. There is no solid ground; you are in the water as the waves both loom and crash.

It’s a reminder again of how radical and unsettling much of this work was in its day. Claude Monet pulls a similar trick in The Break-up of Ice on the Seine, which dates to 1880-81. He centres the viewer out amid the slabs of ice, which are rendered in smears of horizontal paint against the strong verticals of the poplars both standing on the skyline and reflecting in the water. It’s a thrilling piece that seems to look forward to the abstractions of the 20th century and perhaps for that reason, Reinhart, whose taste only went so far in embracing later movements, hoped to sell it in order to fund the acquisition of earlier Monet works. (Reinhart thought carefully about the balance of his collection: he waited 30 years to by Edouard Manet’s 1878 Au café, another work which withholds its meanings quite as assertively as Goya’s did.)

By the time Reinhart met Courtauld and admired Van Gogh’s Self-Portrait with Bandaged Ear, painted in 1889, he had already acquired two of Van Gogh’s works from the same year. They are companion pieces, the only two paintings he made during his stay at the Hôtel-Dieu Saint-Esprit in Arles, where he came after he severed his ear. One is of the ward in the hospital, the other is of the courtyard. The latter seems to balance exterior and interior states, brilliant flowers in ordered gardens against the mostly static figures in the blue shadows of the colonnades. It is painfully beautiful. The former is more uneasy and difficult: figures huddle around a stove in the foreground while all the lines of floor and ceiling lead the eye to the vanishing point of the end wall. You can’t help but notice the empty chair off to the left of the painting.

‘One perhaps learns how to live from the sick,’ Van Gogh wrote to his brother early in 1889. Madness is a poor metaphor for art, but it is a different way of seeing, nonetheless, filtering the things of the world through an intense and unmediated sensibility. What is seen and experienced is powerfully changed: re-ordered, re-articulated, re-imagined.

More than anything, Goya to Impressionism, like the Courtauld itself, validates Reinhart’s moral sense of the value of collecting. It embodies the importance of art that speaks in multiple individual voices, finding new subjects to paint and exploring old subjects in new and artistically radical ways – which is to say, it demonstrates the necessity of art to speak to art. Out of these confrontations of sensibility and technique come new languages, new visions: the provocations of Goya and Cézanne alike can still shock us into infinite surprise and wonder.

Goya to Impressionism will be displayed at the Courtauld Gallery between 14 February and 16 May 2025.