"Il n'y a rien dans ce monde qui n'ait un moment decisif." 

Henri Cartier-Bresson considered the essence of photography to be capturing the decisive moment. This is a workable theory if you're running around shooting strangers on the streets of Paris, but working with models is a bit more complex. A decisive moment cannot exist in a vacuum. There must be a moment before, which makes those moments that follow inevitable and a moment that follows, which is the logical consequence of what preceded.

For me, photography is the art of performing in two dimensions. Just as an actor must create a sense of the moment before and portray the impression of having had a full life before the curtain rose, and follow-through with some overarching objective that doesn’t end at the edge of the proscenium, leaving a shadow lingering on the stage floor, so must a model create a sense of emotional and physical progression within the confines of a static image. The photographer and model must work together to create the moment before and the moment after that define the decisive moment and produce an image with a dynamic sense.

Beyond that, there is only one absolute, incontrovertible, immutable truth in photography: If there isn't a pretty girl in the frame, the picture probably doesn't need to be taken.