The view that knowledge-yielding single-premise deductive inference must proceed from a known premise is very plausible at first blush. In this thesis I explore in detail the possibility that this view is false. I construct a series of challenging cases against the principle of Counter-Closure, which expresses this view. These cases force theorists endorsing a variety of contemporary views to either (i) abandon Counter-Closure; (ii) admit into their epistemology novel and theory-specific kinds of Gettier cases; or (iii) make significant revisions to their theories. I offer considerations that help would-be deniers of Counter-Closure explain away its prima facie plausibility and suggest a suitable theoretical replacement phrased in terms of justification rather than knowledge. Finally, I connect this discussion with debates in the epistemologies of testimony and memory, where analogue principles to Counter- Closure have been recently subjected to critical scrutiny.