In 1940, George Balanchine was a choreographer rich in ideas and short on funds. Even so, he paid the German composer Paul Hindemith out of his own pocket for a short score for piano and strings: a theme followed by four variations. Six years would pass before that music became one of the most influential ballets of the century.

The inspiration reaches back to the Middle Ages, when physicians believed four bodily fluids, or humors, shaped a person's character. Each produced its own temperament: melancholic, sanguinic, phlegmatic, and choleric. Balanchine never set out to illustrate a medical textbook. Instead, he gave each temperament its own physical weather, from sorrowful backbends to buoyant speed, languid wit, and sudden, blazing force.

The ballet premiered on November 20, 1946, on the very first program of Ballet Society, the company that soon became New York City Ballet. Its original costumes were so ornate they nearly buried the dancing, so within a few years Balanchine swept them aside and dressed his cast in simple black and white practice clothes. That bold choice revealed everything: jutting hips, flexed wrists, and classical lines bent into thrilling new angles. It also helped define the sleek, unadorned look audiences still associate with Balanchine today.

This fall marks 80 years since that premiere, and the work has lost none of its edge. Tonight, it reminds us how daring the classics once were, and still are.