Egyptian identity was tied to Arabic fluency, which black slaves lacked.

Evidence

The passage is revealing—Imäm al-Abd was as Egyptian as any other native resident of Cairo, but his physique, for al-Bishrï, contradicts that indigenousness. All the features that made Imäm al-Abd black detracted from his identity as an Egyptian. His physical features belied, at least for the Egyptian audience envisioned by al-Bishrï, his real fluency in Arabic, both classical and colloquial. And historically, language did mark a difference between slaves and Egyptians.As Umad Ahmad Hiläl has written, slaves in all their forms in Egypt had no knowledge of classical Arabic. Even after Circassian-Ottoman slaves were manumitted, the majority remained affiliated with the Turkish-speaking social classes and were fairly isolated from Arabic-speaking groups. Sudanese slaves, the majority of whom came from the non-Muslim territories of the Sudan, communicated with each other in the colloquial dialect. This may well be why Imäm al-Abd presented so stark a linguistic enigma to al-Bishrï and others. — Eve M. Troutt Powell, A Different Shade of Colonialism_…, 789

Categorization

• DEFINE: Shows how language (classical Arabic fluency) functioned as a boundary between Egyptian and slave identity, a useful clarifying point for understanding colonial-era Egyptian society.
• XREF: Connects to the reader’s goal of distinguishing Egyptian vs Sudanese colonial experience — language becomes a marker of belonging that excludes the Sudanese.