The Times states in its style guide that: "Ms is nowadays fully acceptable when a woman wants to be called thus, or when it is not known for certain if she is Mrs or Miss."[6]
The Guardian states in its style guide that: "We use whichever the woman in question prefers: with most women in public life (Ms Booth, Mrs May, Miss Widdecombe) that preference is well known; if you don't know, try to find out; if that proves impossible, use Ms."[7]
That all sounds fair enough to me. To not know this says a lot about who you are.
[hr]
Like flames on fuel...upon metal I drool


