This is a very good question. However, as the question stand, it is almost unanswerable, because neither Greek nor French philosophy is monolithic. There is so much variability among philosophers!; no two agree! Moreover, there were many of them. So, even generalizations will be imprecise to say the least. In light of this, let me just mention a few points that will help you get into this topic.
The two greatest philosophers in the Greek world were Plato and Aristotle. They both believed in what is known as the forms. The forms can be thought of as universal truths. Plato believed that the immortal soul could know these forms. Aristotle believed that these forms could be known more fully through investigation. Hence, Greek philosophy had knowable universals.
When we come to the French, many of their philosophers (post-modern era) have done away with the idea of knowable universals. They have moved beyond things like structuralism. Instead, they say that all knowledge is socially constructed and therefore relative. Some of the famous names in this camp are: Foucault, Derrida, and Deleuze.