Rediscover Constable in his finished work

An exhibition at London's Tate Britain (national gallery of British art) provides an opportunity to look with unusual intensity and attention to detail at the major landscape paintings of the early 19th-century English artist, John Constable.

People sometimes assume they are overfamiliar with Constable. But Constable scholars continue to discover and discuss new facets of his work, lost works resurface, and Constable emerges as an ever more complex and original artist.

The large "finished" canvases that he exhibited at the annual Royal Academy exhibition – "The Haywain" being the most famous – were commonly dismissed in the 20th century as overworked. But to his contemporaries, they had not seemed nearly finished enough. After the apparently spontaneous landscapes of the French Impressionists gained acceptance, Constable's paintings started to look fussy and contrived by comparison.

Twentieth-century art writers argued that the "true" Constable was not seen in his finished exhibition works, but in the working "sketches" painted by the artist as preparatory stages toward these works.

These sketches are exhilarating, free and bold to later eyes. But to Constable they were part of his working process, not intended for public viewing. They were an arena for changes and reconsideration. These preparatory works have a high (and exciting) degree of confidence and swiftness.

The difference between the full-size sketches and the finished paintings is shown here in the case of "The White Horse." Until recently, the sketch was thought to be a finished work. But major cleaning and the removal of later additions – probably not by Constable – have revealed it to be, after all, a sketch.

This discovery was an incentive to stage the current exhibition, offering people an opportunity to come closer in their assessment of Constable to his own idea of his art. It is evident that he wanted to retain the life and vitality of his direct encounters with nature, but also meet the demands of his time for "finish." His own dissatisfaction with his "finished" paintings is apparent. He often continued to work on them after the Academy exhibitions had ended.

• 'Constable: The Great Landscapes' is at Tate Britain in London until Aug. 28. Then it travels to the National Gallery of Art in Washington and later to the Huntington Library in San Marino, Cal.