In studying the past, we should first do all we can to understand it in its own terms, and only then consider possibly anachronistically applying concepts from a later time. But sometimes, such retrospective application can yield real insight. For instance, some time ago I realized that the logical meaning of Aristotle’s two proposition-forming operations of “combination” and “separation” of terms is actually very well explicated by Brandom’s notions of material consequence and material incompatibility (see Aristotelian Propositions).
Philosophers sometimes develop their own very distinctive meanings for common terms, in which case interpreting those terms in the common way can result in serious misunderstanding, and naturally this can also affect the validity of applying them retrospectively. So, for instance, under a “common” interpretation, Hegel’s talk about the concerns of Socrates for Self-Consciousness and Freedom makes little sense. But with a better understanding of Hegel’s distinctive use of these terms, it is much more intelligible. (See also Hegelian Genealogy.)