Is it correct to write:
He wants to explain X concept to the layman, not before warning him ...
Or should I write:
He wants to explain X concept to the layman, not before warning him or her ...
The easy (and for once not inelegant) solution is to evade the issue by using the collective:
EDIT Since use of laity in a non-religious sense has excited considerable comment, I note that OED 1 dates it back to 1832, citing the Jurisprudence of John Austin, a leading philosopher of law:
And for those who object to grounding an argument on the usage of a lawyer, I offer the greatest modern master of English prose style:
I would suggest either using layperson and using either him or her or them which can be used as a singular.
Historically, he can be used to mean he or she, but nowadays I think it's less acceptible due to changing tastes and English being a living, changing language. I've also seen she used meaning he or she and I think that's fine but inelegant.
I would use he or she/*him or her* or they/*them*.
The singular-they has been used in English for a long time, and I think ultimately offends fewer people than just he or just she.