From Walter Benjamin, The Arcades Project, Convolute N--
It is not that what is past casts its light on what is present, or what is present its light on what is past; rather, image is that wherein what has been comes together in a flash with the now to form a constellation. In other words, image is dialectics at a standstill. For while the relation of the present to the past is a purely temporal, continuous one, the relation of what-has-been to the now is dialectical: is not progression but image, suddenly emergent.The dialectical image is an image that emerges suddenly, in a flash. What has been is to be held fast -- as an image flashing up in the now of its recognizability. The rescue that is carried out by these means -- and only by these -- can operate solely for the sake of what in the next moment is already irretrievably lost.