Naji is a buzuk player, a music educator, and a pharmacist. In his Ph.D. dissertation he contrasted similarity based versus rule-based approaches to categorization of and modulation between the scales within the Arabic scale system (maqamat). Following an analysis of 100 songs from the Egyptian repertoire of Arabic classical music of the 1940s to 1960s he outlined a general rule which defines the set of possibilities of modulation from one maqam to another. In addition he built a mathematical model for predicting the similarity between pairs of maqamat. He tested these two hypothesized constructs empirically both quantitatively and qualitatively through experiments and interviews with Arabic musicians.