Question

What school of social thought argues that everything is relative, fragmented, temporary, contingent, ephemeral, and lacks any substantive reality, and thus is generally an anti-positivist perspective?

Answer 1

This would be postmodernism. Basically, this is the theory that is use to describe a very large movement that came about roughly in the late 20th century in the philosophy, architecture, arts and criticism community which marked the move forward from modernism.