Impressionism vs Post Impressionism: The Difference
Impressionism was a real group that exhibited together from 1874 and chased how light looks at a given moment. Post Impressionism was never a group. It is a label a critic invented in 1910, by which time three of its four painters were dead.
That is the real difference. One is a movement with a founding exhibition and a shared aim. The other is a filing category applied afterwards.
If you want to go past the surface
Three that changed how I look at a picture:
Was Monet really the first Impressionist, the painting that may have got there first
Luncheon of the Boating Party, detail by detail, who everybody at that table actually was
The darker truth about Gauguin, the part of the Tahiti story that never makes the wall label
Where the word Post Impressionism comes from
In November 1910 the critic Roger Fry organised a show at the Grafton Galleries in London and had to call it something. He settled on Manet and the Post Impressionists.
Van Gogh had been dead twenty years. Gauguin seven. Cezanne four. None of them ever heard the term, and none would have recognised themselves as members of anything.
So when people ask what the Post Impressionists believed, the honest answer is that they did not agree on much, and they were never asked.
What the Impressionists were actually doing
Painting outdoors, fast, with unmixed colour laid in broken strokes, to record a specific light at a specific hour. Shadows in blue and violet rather than brown. No black.
Subject matter was ordinary and modern: stations, boulevards, riverbanks, people at lunch. The point was the light on the thing, not the thing.
Monet painted the same haystack over and over, not because he cared about hay, but because the light kept changing.
What the four did with it instead
I find this the clearest way to hold it: they inherited the same palette and each one spent it on something different. Structure, feeling, symbol, system. Four incompatible answers, which is exactly why they never formed a movement.
Cezanne kept the colour and threw out the fleetingness. He wanted structure, the solid shape under the surface, the apple as a form rather than as a moment.
Van Gogh kept the colour and used it for feeling. The brushstroke stops describing light and starts describing an internal state.
Gauguin kept the colour and used it for symbol. Flat areas, arbitrary hues, meaning imposed rather than observed.
Seurat kept the colour and turned it into a system, applying optical theory dot by dot until spontaneity was gone entirely.
Four incompatible answers to the same inheritance. Which is precisely why they never formed a movement.
How to tell them apart in front of a picture
Ask what the painter was chasing.
If the answer is a passing effect of light, and the brushwork is loose and broken and the whole thing feels like it was seen rather than composed, that is Impressionism.
If the colour is just as bright but the picture has been deliberately built, if shapes are simplified, outlined, patterned or systematised, that is Post Impressionism.
Rough guide: Impressionism dissolves the object into light. Post Impressionism puts the object back together on the painter's own terms.
The dates, honestly
Impressionism: first group exhibition 1874, eight shows in all, the last in 1886.
Post Impressionism: conventionally 1886 to about 1905, which is to say it starts the year the Impressionists stopped exhibiting together and ends when Fauvism arrives.
The two overlap in real life. Cezanne showed in the first Impressionist exhibition. Painters do not change category on a scheduled date.
The questions that come up about both
Was Van Gogh an Impressionist? No, though he learned from them in Paris. He is filed under Post Impressionism.
Is Pointillism the same as Post Impressionism? Pointillism is one branch of it, the one Seurat invented.
Who named Impressionism? A hostile critic in 1874, taking the word from a Monet title. It was meant as mockery.
Did the Post Impressionists know each other? Some did. Van Gogh and Gauguin famously shared a house for nine weeks. It ended badly.
Which came first? Impressionism, by roughly a decade.
Both movements were named by other people
One was named by a critic making a joke in 1874, the other by a critic filling in a catalogue title in 1910. Neither group chose its own name, and both names stuck anyway.
Full explanations of Impressionism and Post Impressionism are here, and the painters themselves: Monet, Van Gogh and Cezanne.
If you want to know who really painted the first Impressionist picture, that one is here.