The title of this essay1 came by way of, "Diderot, Brecht, Eisenstein", an essay by Roland Barthes to which I shall refer later. Recent theory has been very interested in the facts of which my extemporaneous substitution of one phrase for another is an instance: meaning is only ever produced in difference, and the final closure of meaning is only ever deferred — the combination of observations which Derrida enshrined in his neologism, différance, but to which C. S. Peirce had already referred in his notion of "unlimited semiosis". Meaning is never simply "there" for our consumption, it is only ever produced in a process of substitution of one term for another in a potentially limitless series. In the social world, however, meaning must come to rest somewhere; what is it that sets limits on the meanings of images?