What is grammar?

Grammar tells what words do in sentences and about the way sentences are made. It is essential for the user of the English language to learn grammar in order to write and speak clear and correct English, because grammar deals with rules that all educated people know and recognise.

In a way, grammar is good manners. With the aid of grammar one is able to speak and write in a form that all educated people understand.

-Milon Nandy, Refresh Your English, Rhythm Publishing, 1997.