What, or who is an Arab? There is no simple or final answer, and inevitably Mr. Carmichael, for all his background and insight, is thrown back at last upon timid-seeming generalities and the vaguest sort of conjectures. If (as he says) one takes the case of a large body of people sharing the same language and religion, living in the same general area, and claiming a common history, and then one supposes this body of people to be permeated by Western ideas, including nationalism, it would appear a foregone conclusion that they would have formed a cohesive nation by this time. Not so the Arabs. They have remained ""on the verge, perhaps, of ethnic crystallization."" The reasons must lie somewhere within the complex but glorious history of Islam, and Mr. Carmichacl has labored valiantly--and always interestingly--to bring them out. It is a story little known to Europeans and Americans, and well worth closer attention.