I defend an internal history of philosophy that prioritizes philosophical reasons over cultural factors. This approach contrasts with a broadly contextualist endeavor invoking cultural factors without clear ground. I argue that the latter path is either too permissive or leads to aiming at a complete historical account. Neither way is acceptable: the former obliterates the correctness of interpretation; the latter dissolves history of philosophy in general history and is practically impossible. Instead, the internal history I propose – based primarily on Michael Frede’s and Maurice Mandelbaum’s historiography – prioritizes philosophical reasoning and appeals to external contextual factors in a principled way when it is necessary to supplement philosophical considerations.