I summit this post as a little proglomena to discussing some of my reading for my PhD, especially Heidegger...
I want to outline my position regarding epistemology. I have just completed a BA in media and communication and the issue of 'what is real' was a major theme throughout my three years of study. There are of course several competing theories answering the question what is real.
Firstly naive realism:
This asserts that the real world is out there to be discovered or named by human beings. A criticism of naive realism is that it attributes objects with intensions, how for instance can a rock 'tell' us what it is.
This approach at its most extreme contests that reality is a construction of the human mind. Although in a softened form it Kant be found for example in Kant's assertion that humans create the structure of the world a priori before the world is revealed to them. The main criticism of this approach is a common-sensical one. for example it is said that Samuel Johnson refuted Berkely's idealism by kicking a stone - "there," said Johnson, "I have just refuted Berkely's hypothesis."
This approach contends that reality is a mix of environmental factors (naive realism) ordered by social conventions (idealism). For instance the Linguist and co-founder of semiotics Ferdinand de Saussure asserted that language creates the meaning of reality. This - it is a bit of both - approach seems more plausible that either naive realism or idealism, however there problem as I see it is very much bound up with representation systems, which downplays the fact that reality has a very palpable immediate component.
This is why I find the epistemology of the American pragmatist philosopher Charles Sanders Peirce, especially his notion of the fundamantal categories of firstness, secondness and thirdness. For me Peirce really nailed the problem of epistemology, but the power of his analysis is really yet to be fully appreciated. For example, if you read Heidegger's Being and Time, bearing in mind Peirce's categories there are less problems in picturing what Heidegger has in mind. Heidegger to my mind never completely successfully addresses the difficulty of communicating pre-representational systems through the language of philosophy. Peirce I think can be particularly helpful in this respect because he developed an approach which can describe the kind of mental paradigm shifts Heidegger is calling for his readers to attempt in order for them to understand Dasein.
Links to my work in this area
For more on a structuralist take on representation this see this essay, which offers an account of Saussure's semiotic.
and my undergraduate dissertation that discusses Peirce in Chapter 5 and more on my particular epistemological position.