What makes avant-garde avant-garde?

[Vincent A. Maeder]

Malignd wrote >I think the term is meaningless, a perhaps once-useful
term that no longer has currency except in historic terms; e.g., in
speaking of what was once considered avant-garde.<

The concept of invention, evolution and revolution in art and literature
still has purpose.  Perhaps it is difficult to parse such changes until
after the events have occurred.  For the sake of argument, assume we can
recognize significant and important innovation in literature; what would
it look like?  Unless it's one of those, "I know it when I see it"
thingies...

I would hazard to say that if such a concept "seems now precious, even
ludicrous" that we are saying literature is dead; or at least in code
awaiting the defibrillation of genius.

V.