The paper argues that there is no valid closure principle that can be used to infer sceptical conclusions. My argument exploits the Gettier Intuition that knowledge is incompatible with accidentally true belief. This intuition is interpreted as placing a constraint on beliefs that can count as knowledge: only beliefs which are based on reasons that are relevantly linked to the beliefs’ truth can qualify as knowledge. I argue that closure principles are to reflect this constraint by accommodating the requirement that a subject's belief p needs to be based on her competent derivation of p from a known q. The emerging account is finally argued to reconcile Dretske's anti-closure intuitions with the intuition that we can extend knowledge by deduction, while simultaneously blocking closure arguments for scepticism about the external world.