As Hal Foster, editor of ''The Anti-Aesthetic: Essays on Post-Modern Culture, '' (New York: Bay Press. 176 pp. $13.95 cloth. $8.95 Paperback), suggests, the word ''postmodern'' may sound illogical: Doesn't modern mean contemporary? How can we talk about something postmodern - that is, something beyond the present that already exists? But modernism doesn't refer to a condition of time. Instead it defines an aesthetic.
A central characteristic of the modernist aesthetic is fragmentation. This fragmentary vision of the world is seen in the broken planes of Picasso's Cubism and in the shards of sense pieced together by T.S. Eliot in ''The Waste Land.'' Here was the shock of displacement; mourning for the wholeness shattered by an increasingly industrialized society in which man was alienated from the natural world. The fragmentation of society induced specialization among workers, intellectuals, professionals. And so modernist culture tried to describe (by breaking up the picture plane or conventional narrative sense, for example) the upheaval and isolation that compelled Eliot to write, ''These fragments I have shored against my ruins.''
But the specter of fragmentation has hovered overhead for so long that it has lost its dour punch, its anxiety. Every high school student is taught the merits of ''The Waste Land.'' The revolution of Cubism, once seen as a disorienting demonstration against an outmoded order, is now commonplace. The sense of the fragmentary is our air and water. While Eliot ended his first great modernist poem, ''The Love Song of J. Alfred Prufrock,'' with ''Till human voices wake us, and we drown,'' the consequences of fragmentation - the bewildering specialization of professions and disciplines, the isolationism of academic thought and language from daily life and speech, the equivalent specialization in the arts that has led to their general inaccessibility - have become a fluid environment in which many have learned to swim.
The fragment is redefined as the gram by one postmodern spokesman, the French philosopher Jacques Derrida. Think for a moment of the fragment as a piece broken away from a whole that has depth, solidity - the mass of complete worldly knowledge. But the gram is that piece of information now floating free among many other pieces. These grams are meant to be read across their floating surfaces in an illimitable combination of meanings. No doubt this calls up pictures of information networks, of computer systems. And why not? Just as modernism found its model in the idea of an industrial world, postmodernism is linked to our present technology.
It's clear from Foster's fascinating anthology of essays that much new cultural activity focuses on the interchangeability, the sudden shifts and innumerable grafts of meanings made available by the notion of the gram. Pastiche, for example, is a standard postmodern practice; different historical styles are mixed together in one work. We see this repeatedly in new buildings and paintings, in new literature and dance. Foster's essayists speak of this as a liberating technique from modernism's nostalgia for authority and a desire to open up new possibilities for an audience's comprehension. Interestingly, these essays often suffer from the modernist tendency of specialization that they criticize. They are filled with jargon that only the highly tutored comprehend. But they do point out the conflicts and dangers of postmodernism, as well as its promise. What the consequent moral, aesthetic, and cultural meanings are will be my subject in the months to come.