ABSTRACT Philo of Alexandria didn’t use lofty words and impressive thoughts to comment De Decalogo. But, as Nikiprowetzky asserts, philosophy and rhetoric can be remotely felt in its background. Philosophy shapes the thoughts that give his commentaries substance, and rhetoric shapes the harmony and power of their expression. For him, Philo’s style was often admirable. And it wasn’t just a question of eloquence or style. As I will show in this paper, Philo creatively used forms of argumentation as practiced in the progymnasmata and fixed in the Greek textbooks of prose composition and rhetoric, namely those related with thematic elaboration. Exploring the argumentative texture of De Decalogo in its multiple kinds of logical and qualitative reasoning, I found rhetorical coherence and effectiveness in the discourse as a whole and in the particular units that compose it. My critical analysis brought to the surface types of argumentative topics and structures which sustain my conviction that the essence of true rhetoric is pervasive in Philo; a learned process of argumentation that is more than a taxonomy of linguistic devices and persuasive strategies.