Singular Epicene Antecendents

Partially because English lacks some of the language devices that are incorporated in the development of some other languages, there exists an ambiguity within our usage of singular epicene antecedents....... For example: someone left "their" book at the restaurant........Is this person male or female? "Their" implies more than one person, doesn't it? I was taught in elementary school to use the masculine pronoun unless the antecedent has been already established.......EXAMPLE: Mary left "her" book at the restaurant....... When the antecedent is unclear, we say "Someone left "his" book at the restaurant.... but never "someone left "their" book at the restaurant, unless the book belonged to more than one person....... There must be an acceptable workaround, but I see scant evident of this in modern English usage.

{Three factors appear to contribute to speakers' choice of pronominal: presuppositions about gender roles associated with the referent, notional number of the referent, and the extent to which the referent can be posited as a specific individual. The idea that there is a gap in third person singular pronouns in spoken English is criticized.} Michael Newman LANGUAGE IN SOCIETY

My attempt to discuss this, and other idiomatic elements of conversational...and now written.....Language....has led to intensively argumentative disagreements with many people that I think lack the 'language' skills to express their thoughts, ideas or feelings......This 'lack' initiating hostile, even retributive, responses.......