Grammatical rules for the use of commas are extensive but include using commas to separate words in a series of three or more, using commas to separate two adjectives when they are interchangeable, and using a comma after certain words at the beginning of a sentence. Complete grammatical rules for the use of commas are found on GrammarBook.com, Grammarly.com and ThePunctuationGuide.com as of 2015.
Find grammatical rules for the use of commas on GrammarBook.com by clicking Punctuation Rules on the homepage and then clicking Commas on the next page. The next page displays comma rules and examples of comma usage. To take a quiz on comma usage, click Commas Quiz near the bottom of the page.
Find grammatical rules for the use of commas on Grammarly.com by clicking Handbook near the bottom of the homepage and then clicking Comma on the next page. The page displays links to comma rules such as comma usage and comma splices.
To find grammatical rules for the use of commas on ThePunctuationGuide.com, click Comma on the homepage. To view a comma rule, click a link on the next page. Rules include mechanical uses of commas, rules for commas in lists and how to use commas in compound sentences.