The grammatical controversy as to how to say "I am not a terrorist" in Arabic to which Ben Zimmer refers, is, I think, not so much about what the correct grammar is as what sort of Arabic to use. As I understand it (and Arabic is not exactly my best language), it is definitely the case that a noun such as "terrorist" should be in the accusative case when it is the predicate nominal in a negative predicate. This rule, however, is a rule of Classical Arabic: the modern colloquials do not have the three-way case distinction of Classical Arabic and therefore have no such rule. What the debate is really about, then, is whether T-shirt slogans should be in the classicizing "Modern Standard Arabic" or in a more colloquial variety.
Addendum: Readers with greater knowledge of Arabic than mine have explained that the issue of what is correct grammar and which variety of Arabic to use are intertwined because the verb lastu "I am not" is used only in Modern Standard Arabic. It is not found in any of the colloquial varieties. Therefore, if you use lastu you also need to put "terrorist" into the accusative case. If you don't use the accusative case of "terrorist", you must be writing in a colloquial variety of Arabic and will therefore use a different negative construction, one that does not use the verb form lastu.
Posted by Bill Poser at August 31, 2006 10:19 AM