The purpose of this thesis is to investigate and dissolve the puzzles and paradoxes of irrationality in thought and action. The project is divided into four sections: a general introduction, and three chapters. The introduction broadly outlines the nature of the issue, which is then broken down in the introductions to chapters one and two respectively. The first chapter consists in a detailed analysis of a kind of irrationality in thought, namely self-deception. The paradoxes of self-deception are taken to be generated by the view that self-deception is intentional: that is, one must intend the deception. Proponents of this view argue the self-deception can be adequately explained without the presence of an intention, and hence is not parad...