I'm writing a story which takes place in a fictional town called "Aherville" in which all the residents are observant Jews. In the third-person narration, I mix past and present tenses. Specifically, when referring to something done by a character in the narrative, I use the past tense; but when referring to Jewish traditions, I use the present tense. For example, I might write "In Aherville, everyone celebrates Shabbos every week," but a couple of sentences later, write "Zindel felt hungry because he hadn't eaten all day." A reader is arguing that this usage is ungrammatical; she argues that all tenses must match in order to make the narrative voice consistent. I disagree. I've been looking for an authoritative citation to show my friend, but I haven't had any luck so far. Could anyone here direct me to such a citation? Alternatively, if I'm the one who is mistaken, then it would be very useful to tell me that. Thanks very much for any help.