Antifoundationalism is the undermining of traditional claims for the existence of self-evident foundations that guarantee the validity of knowledge and truth, and establish the possibility of determinate communication.

In its extreme forms, the (poststructural) claim is that the workings of language inescapably undermine meanings in the very process of making such meanings possible, or else that every mode of discourse constructs or constitutes the very facts or truths that it claims to discover.