Which of these two canvases came first is debated by scholars. Did Matisse start with the simpler version and like it so much that he deemed it finished, and so switched to a second canvas to make the richer if more conventional Neo-Impressionist medley he originally intended? Or did he paint the more heavily worked canvas first and then, attempting something more pared down, lose his nerve and leave the second unfinished? Either way, Matisse was already beginning to use copying as a way to take the same motif to different pictorial conclusions, shifting from opulent to austere, or austere to opulent. In the case of two 1906 “Young Sailor” paintings, the first can be read as an overworked farewell to Fauvism, while the second cuts to the chase, conveying its subject with consummate abbreviating ease against a flat pink background as if dispatched in a single work session. (Its simplicity apparently made Matisse a little uneasy; when he showed these canvases to the collector Leo Stein, he dissembled briefly, saying that the second had been painted by a rural letter carrier.) Meanwhile he seems almost to have abandoned the 1909 “Seated Nude,” with its patchy color, flurries of pencil and disturbing doll-like face, for its more robust twin of the same year, “Nude With a White Scarf,” more conventionally fleshed out in paint and thick black lines.

It is possible to spend your entire visit in the second and third galleries of this mesmerizing exhibition, mulling over the sailors, the nudes with white scarves, the more regal nude with attendants of “Le Luxe I” and “Le Luxe II” of 1907-8 (Matisse’s “Birth of Venus”?) or the contrasting psychological chords and spatial treatments of the Laurettes. The Museum of Modern Art’s magisterial “Goldfish and Palette,” with its fractured, quasi-Cubist transparencies and incessantly scratched paint, overpowers its more demure cousin, “Interior With Goldfish” (both 1914), until you notice that in this second work the hot orange of the goldfish glimmers subversively through almost the entire surface.

And it is almost shocking to see that the Modern’s great, sketchily painted, nearly all-blue “View of Notre Dame” (1914) has an unlikely fraternal twin from the same year: a relatively realistic view of that cathedral that might almost be a blowup of a postcard except for the daring brevity of its watercolor-thin pastel colors and frequent passages of exposed canvas. Both paintings challenge conventional notions of finish, though from almost opposite directions.

But there is much more on offer. Two relatively comfy views of Matisse’s first hotel room in Nice are traduced by the grandeur of “Interior With a Violin,” a larger third version whose prevailing shades of black dramatically highlight the bit of sunbaked beach visible through the louvered shutters. Three views of the beach at Étretat, on the coast of northern France, revisit a scene beloved by Monet, presenting different catches of the day while experimenting with deep space and variously notational ways of indicating pebbles, bluff and water.

In the 1930s Matisse began having black-and-white photographs taken of his paintings at regular intervals as he worked on them. This was clearly another way to preserve artistic ideas for future use, but he also sent photographs to clients and further valued them as proof against critics’ claims that his paintings were casually dashed off. In 1945 he went so far as to exhibit six paintings, each surrounded by its matching photographs, at Galerie Maeght in Paris. The seventh gallery of the Met show presents three of the Maeght canvases amid their evidentiary pictures. They establish that Matisse’s progress was often grueling and yet, especially with the ornate vessels and shell in “Still Life With Magnolia” (1941) and the sleeping model in peasant blouse of “The Dream” (1940), he worked through his difficulties to a final image that exudes consummate freshness and ease.

By the time you reach this point in this astounding exhibition, it is clear that Matisse’s paintings are almost always hard-won distillations, but it is nonetheless marvelous to see the process so forthrightly chronicled. His ecstasy was built on numerous forms of transparency.