Comment by SwedishDungeon

He's saying the enslaver wants contradictory traits in the slave, intelligence and subservience.

This isn't contradicted by millennia (not centuries) of slavery because it was forced on the enslaved populations against their will.

> Or is the author arguing that the people who were enslaved did not have human-level intelligence

He gives an example of "a clever Greek philosopher slave of a less intelligent Roman slaveholder." Does it sound like he's arguing that Greeks were not of "human-level intelligence"? No.