The Plausibility and Limits of the Closure Principle

The closure principle is a topic of great debate and much controversy for the last four decades. The closure principle has many different forms and variations depending on contexts, but the central problem is always the same: is knowledge closed under entailment? In this paper I examine the plausibility and limits of the closure principle on the basis of a detailed analysis of different epistemic routes to knowledge and different ways the actual world could be. The conclusion of this paper is that we can expand our knowledge deductively only when the antecedent is knowledge by acquaintance or a priori knowledge. Therefore the closure principle is plausible, but limited. This conclusion can provide us an explanation for our intuition that we can expand our knowledge base through deduction, while avoiding paradoxes and skeptical arguments related to closure.