In formal writing, do I need to Capitalise the title of the person I'm referring to ? For example,
I wrote to Professor Cassest yesterday.
Is it correct to capitalise both Professor and Cassest?
My answer is based on American English rules. What you ask concerns both capitalisation of titles and capitalisation of occupations. Let's look at the rules first:
1) Titles - Capitalize titles when they are used before names, unless the title is followed by a comma. Do not capitalize the title if it is used after a name or instead of a name.
The president will address Congress.
Chairman of the Board William Bly will preside at the conference.
The chairman of the board, William Bly, will preside.
The senators from Iowa and Ohio are expected to attend.
Also expected to attend are Senators Buzz James and Eddie Twain.
The governors, lieutenant governors, and attorneys general called for a special task force.
Governor Fortinbrass, Lieutenant Governor Poppins, and Attorney General Dalloway will attend.
2) Occupations: Do not capitalize occupations before full names.
director Steven Spielberg
owner Helen Smith
coach Biff Sykes
Sometimes the line between title and occupation gets blurred. One example is general manager: is it a title or an occupation? Opinions differ. Same with professor: the Associated Press Stylebook considers professor a job description rather than a title, and recommends using lowercase even before the full name: professor Robert Ames.
Resource: "The Blue Book of Grammar and Punctuation"