Can Heidegger be understood?

Heidegger's writings are by many thought to be irretrievably obscure. This is not true of Sein und Zeit. In order to show this, I explain what Heidegger means by ?ontology?, ?preontological knowledge? and ?preontological mistake?. These explanations show that there is nothing in Heidegger's conception of his enterprise which makes it impossible that Sein und Zeit should be clear. Since the explanations require discussion of specific theses, I also show that Sein und Zeit is, at least in part, clear as actually written