This study examines Aristotle's concept of separation (chorismos) and explores a seeming contradiction within his thought regarding the definition of truth and scientific methodology. On one hand, in the Metaphysics, Aristotle defines truth as a correspondence with reality, where truthfulness depends on correctly joining or separating things according to their actual state. On the other hand, in the context of mathematics and geometry, he suggests that observation is most effective when treating non-separate entities as separate. This raises a significant epistemological problem: how can a methodologically incorrect or false assumption lead to truth, which remains the ultimate goal of observation? The text highlights that this issue is not merely a peripheral philological concern but represents a profound internal tension that has resonated throughout the history of European thought. The analysis focuses on the Greek terms chorismos and chorizo and their implications within the broader framework of Aristotelian ontology and the philosophy of science.