This thesis is made up of five chapters: one integrative chapter, and four discrete essays. Each of the four essays is concerned with some aspect of epistemic structure. The first essay, Risk, Doubt and Transmission, explores structural analogies between testimonial transmission and closure principles. The second, Testimonial Pessimism, traces the connections between moral and aesthetic testimony's putative shortcomings and the philosophy of language. The third essay, Epistemic Ambivalence, argues that the ideology of higher-order defeat is paradox prone, and as such, ought to be rejected. The fourth essay, Tragedy and Rationality, makes vivid some costs associated with endorsing an anti-akratic constraint on rationality.