Authoritarian - authoritative

Authoritarian and authoritative have been confused. Both are adjectives and both are derived from the same original word, authority. One is a term of praise (use it when you want to pay a compliment to someone) and the other a term of dispraise, so they should not be confused.

• Authoritative is the term of commendation. It is a virtue in academic circles. Authoritative means 'with authority', in the sense of 'having sure knowledge', or 'being a recognised expert'. To say that a textbook is authoritative is to say that it can be trusted; it is right; and that it should be respected. For some of the etymological background to this, see authority.
• Authoritarian is not usually a term of praise - it is the opposite. Authoritarian means 'preferring authority (in the sense of 'discipline') to freedom'. It is most commonly used as a pejorative term to describe someone who believes in dictatorship. Authoritarian is also used as a noun to mean 'a person who behaves like a dictator, or a bullying official, teacher, policeman or the like'. Both Stalin and Hitler ran authoritarian regimes; both were authoritarians.

The adjective meaning 'to do with an author' is authorial. Examples of its use include the description of a writer's style as "the authorial voice", or of the writer's character as "the authorial persona".

You may also like to look at Authorise.