This thesis examines and analyses notable arguments for and against the view that de se attitudes pose a problem for traditional accounts of propositional attitudes. On traditional accounts, the contents of attitudes are propositions. David Lewis challenges this notion and argues that de se attitudes have unique features that cannot be accommodated on traditional accounts. He offers a revisionary centered worlds semantics for de se attitudes by proposing that the contents of attitudes are properties. The main argument in this thesis is that de se attitudes are problematic for traditional accounts and Lewis' centered worlds offers us the most resources to account for de se puzzles and cases. In chapter 1, I introduce traditional accounts of attitudes. Chapter 2 outlines Lewis' centered worlds and we discuss the reasons he abandoned his possible worlds model. Then, we analyze arguments for the view that de se attitudes pose a problem for traditional accounts in chapter 3. Chapter 4 discusses the arguments against the view that de se attitudes need a special semantics and I offer ways a Lewisian can resist the force of these arguments.