Ms. was coined as a title for women analogous to Mr. for men, implying nothing about marital status. In this respect it is crucially unlike the traditional forms Mrs. and Miss.
In a recent post, linguistlaura says a friend of hers faced the choice of Mrs. or Ms. – no Miss – in a website’s dropdown menu. This, Laura writes, undermines the point of having Ms., because:
if it’s used in opposition to Mrs., then it implies ‘unmarried’, becoming synonymous with Miss. For it to retain its purpose, it has to be the only option (with Mrs. and Miss not available) or the Mrs./Miss system must be available: both options must be present.