First, the critical verdict: The Royal Academy's new exhibition, "The Real Van Gogh: The Artist and His Letters" is a must-see affair — if you're in London before it closes April 18.

Not only does it contain by far the most impressive array of work by this supreme artist to be seen in London in 40 years, the show even lives up to its ambitious title.

This isn't just a lot of fine van Goghs, though it is that — on display are 65 paintings, among them many of his most celebrated pictures plus half as many drawings. It's an intelligent exhibition, which introduces you to a more subtle view of van Gogh's mind and work.

There's a downside: You can't just relax and enjoy the show. You have to pay close attention to comparing and contrasting drawings and paintings, and to reading the numerous texts. The upside: If you do, you'll discover a great deal about van Gogh, the man and the artist.

The basic premise of "The Real Van Gogh" is to place side-by-side versions of the same subject in different media: oil paint, drawing and words. Often, Vincent would not only execute a certain idea in oils, sometimes repeatedly: He also would draw it in pen and ink, perhaps in a miniature sketch inserted into one of his letters, and describe it in the text.

Occasionally, the exhibition manages to line up all three versions — drawing, painting, letter and sketch — as it does with the marvelous "Cypresses" of June 1889. That comparison reveals that the drawings aren't simply an imitation of the paintings; they are translations into another visual language. The process is similar to a composer presenting the same musical concept as, say, a string quartet and a full symphony.

POWER WAVES

It's not that one is better than the other, they just function in different ways. Sometimes, the drawings are more powerful and controlled than the equivalent painting hanging beside them. That's true of the superb drawings of the swirling seas at Saintes-Maries-de-la-Mer from July-August 1888.

What this kind of comparison shows is that van Gogh was an extremely thoughtful artist. Each brush stroke and color note was pondered (as the texts of the letters often reveal). He was, in some ways, the opposite of his public image: a crazed bohemian flailing at his canvases in a frenzy of inspiration.

Even though his pictures look as if they were done at a furious pace, and they frequently were, everything about a van Gogh — each flourish of the pen or thick juicy brush stroke is — considered and exactly right. That's what makes them so strong.

TWO VINCENTS

So, which was the real Vincent? The intellectual, refined master or the hard-drinking oddball who mutilated his ear? Both. This exhibition helps us to understand how they coexisted.

The common factor is intensity — the hallmark of his art and his existence. Van Gogh spent much of his waking life making immensely complicated calculations about shape and color; in one letter, he complained that these left him feeling dazed.

The fact that he was often in an abnormally heightened mental state was both a help and hindrance. It's hard to imagine that otherwise he would have created so much so rapidly. (This exhibition and his whole output consist of barely 10 years' work.) Ultimately, his racing mind — and its fragility — was what made his career short.

"The Real Van Gogh: The Artist and His Letters," which is sponsored by BNY Mellon, runs from Jan. 23 through April 18 at the Royal Academy, London.

Martin Gayford is chief art critic for Bloomberg News Service and author of "The Yellow House: Van Gogh, Gauguin and Nine Turbulent Weeks in Arles."