Many of Cicero’s translations of Greek concepts (assent, comprehension, quality) have become common terms in philosophy but also in ordinary language in many European countries. Some of them, pertaining to epistemology, ethics, or physics, are studied in this chapter to show why and how Cicero set out to create a Latin philosophical vocabulary. He wanted to extend the supremacy of Rome to an area formerly reserved to the Greeks. He tried to avoid technical terms or neologisms and preferred open notions to closed concepts. He aimed at conveying the complexity of Greek philosophical doctrines in Latin and sometimes brought out certain nuances which did not exist in the Greek terms (as in the case of probabile). Cicero’s originality as a philosopher does not lie in creating a new system but in providing philosophy with a new language and in promoting the idea that philosophy was not the privilege of Greek culture but a field open to human ingenuity.