A polite person shows good manners toward others in his speech and actions; he is well bred and gracious. A polite individual avoids being rude as a result of training and because he is aware of the demands and requirements of civil manners. A courteous person is not only polite; he makes an active effort to be kindly, graceful, dignified, and poised. In most instances, the two words are interchangeable, but courteous is a stronger word than polite and suggests a fundamental attitude toward others, whereas polite relates to surface manners only: It is polite to say "Good morning" to someone; it is courteous to treat others with respect and kindness.
Dictionary of problem words and expressions. Harry Shaw. 1975.