The problem of realism and anti-realism is one of the perennial philosophical problems. Basically, the problem concerns the relation between representation and reality. Philosophers have long debated these sets of problems, and it seems no agreement is possible for any time soon.
Truth is there, and humans can know it all.
Representations and reality can become one and the same. Anti-realists, however, are skeptical of the idea. Truth there may be, but it is not ultimately approachable by humans. Representations and reality always diverge. More specifically, his view is that there is a dynamic interplay between the Real and the Representation such that one does not collapse into the other, and at the same time one is not radically separate from the other either.