This article inquires into the specific differences between Plotinus' and Dionysius' negative theologies and their contemporary philosophical significance. The comparative analysis looks beyond their general similarities to focus on their respective features. Its main thesis is that while Dionysius' negative theology aims at attaining mystical knowledge of God, Plotinus' version is intended to dispel the illusion that man can attain henosis. The contemporary interpretation puts Plotinus' and Dionysius' negative theologies in the context of analytic epistemology. It is suggested that although both can be understood as criticisms of the epistemology of propositional religious belief, Dionysius' analysis of mystical knowledge of God is closer to virtue epistemology while Plotinus' approach to human ignorance of the One is more similar to knowledge-first epistemology.