Which sort of idealism is defended by Plotinus? In this article, I want to prepare an answer to this difficult question by addressing the issue of sense-perception. As is shown in the paper, Plotinus neither subscribes to a representationalism nor to a naïve realism, nor does he formulate a subjective projectionism. Instead, sense-perception works on the basis of an interconnectedness between all bodily entities provided by the cosmic soul. Plotinus uses the Stoic term of sumpatheia to characterize this interrelatedness. His idealism is hence a monistic one.