Single Premise Deduction and Defeat

Abstract

Preface and Lottery paradoxes have shown that competently deducing a novel conclusion from multiple justified premises does not necessarily result in a justified belief. However, those paradoxes do not arise if only a single premise is used. Yet, in recent years, justification closure for single premise deduction has also been challenged. Schechter has presented a case that, according to him, thwarts any attempt to formulate a general principle that links competent single premise deduction to justification. This paper develops a justification closure principle for single premise deduction that accommodates Schechter’s case, thus showing that his pessimism regarding the possibility of such principles is mistaken. I also argue that an alternative reply to Schechter’s case fails and that safeguarding justification closure constitutes progress for establishing knowledge closure for single premise deduction.