Constructivism and postmodernism endorse and anti-realist metaphysics. Once we abandon the fruitless search for objective reality, so the argument goes, we can devote ourselves to making our beliefs more efficacious than they were before. We can do this because we have given up truth-as-correspondence, and have embraced the claim that what makes a belief right is just that experience has taught us that it works. In short, because our claims to truth (and thus knowledge) refer to utter contingent accounts of reality, it follows that they are only contextually true. As such, any claim to an invariant foundation (an objectively knowable external world, for example) for knowledge is met with skepticism. Instead, knowledge ought to be concerned with the local and specific (contextual) rather than the context-free and totalizing general.
"Anti-realist Epistemologies in Education,"
Journal of Contemporary Research in Education: Vol. 7:
1, Article 5.
Available at: https://egrove.olemiss.edu/jcre/vol7/iss1/5