Historically, as Art and Culture became self-aware, each generation
tried to claim its own territory, swinging back and forth from head to
heart, from classical to romantic, from objectivity to subjectivity,
from modern to post-modern, from idealistic to cynical. And back again;
and back again. In shorter and shorter periods.
Eventually it becomes necessary to find something that is not just a reaction to its opposite, but that can embrace polarities by rising above them, or shatter them by diving below them. Something that has some chance in hell of enduring.
The easiest thing is just to lift this from Wikipedia:
...asserted that “the postmodern culture of relativism, irony, and
pastiche" is over, having been replaced by a post-ideological condition
that stresses engagement, affect, and storytelling.
The prefix "meta-" here referred not to a reflective stance or repeated rumination, but to Plato's metaxy, which denotes a movement between opposite poles as well as beyond them. Vermeulen and van den Akker described metamodernism as a "structure of feeling" that oscillates between modernism and postmodernism like "a pendulum swinging between…innumerable poles"
"...grand narratives are as necessary as they are problematic, hope is not simply something to distrust, love not necessarily something to be ridiculed."
[That last line starts to sound not unlike Howard Barker!]
In 2011, Luke Turner published a Metamodernist Manifesto. The
manifesto recognised "oscillation to be the natural order of the world"
and called for an end to "the inertia resulting from a century of
modernist ideological naivety and the cynical insincerity of its
antonymous bastard child." Instead, it proposed metamodernism as "the
mercurial condition between and beyond irony and sincerity, naivety and
knowingness, relativism and truth, optimism and doubt, in pursuit of a
plurality of disparate and elusive horizons." The text cited the work
of Vermeulen and van den Akker, and concluded “we must go forth and
oscillate!” Turner later credited his manifesto to the actor Shia
LaBeouf as part of the pair's wider artistic collaboration.
[Of course this makes and gives sense to the actor, who, as Antonin Artaud would have it, is always a moving point oscillating between heaven and hell.]