5 ideas
A photograph succeeds when the photographer recognizes, within a fraction of a second, both what an event means and the precise arrangement of forms that expresses it. Content and geometry peak together only for an instant. The shutter must fall at that convergence, not merely when something interesting is happening.
Composition must be felt and resolved at the moment of shooting, because the geometry of a scene exists only in that instant and shifts with a millimeter of the photographer's movement. Cropping or rearranging afterward in the darkroom cannot rescue a badly seen picture. It substitutes calculation for vision and destroys the proportions that were actually perceived.
Unlike a writer, who can reflect and revise, the photographer deals with things that are constantly vanishing, and a missed moment can never be recovered. Cartier-Bresson therefore treats the photographer as a hunter who must stay alert and ready to pounce. Preparation and attention have to precede the event because there is no second attempt.
To capture life as it is, the photographer must move unobtrusively, approaching softly on tiptoe with a velvet hand and a hawk's eye. The aim is to avoid altering the scene by being present: no flash, no staged poses, no elbowing in. Once people notice they are being observed, the authentic situation is lost and the photographer must wait until they forget the camera.
In the early 1930s the young Cartier-Bresson acquired a small Leica, which he came to describe as an extension of his eye. He spent whole days roaming the streets, 'strung-up and ready to pounce,' determined to 'trap' life in the act of living within a single frame. This period produced his first major street photographs, and he offers it as the origin of the decisive-moment method.