Commas

Do not use commas to separate parts of measurement (7 lbs 2 oz). Use the metric system, as a rule.

Use commas before "and" in lists, for example, height, width, and depth.

Use commas between groups of three digits, for example, 2,234.

Use commas to set off a reference in a parenthetical comment (Walden, 2012).

Use commas for seriating within a paragraph or sentence.  For example, "three choices are (a) true, (b) false, and (c) don't know." Use semicolons for seriating if there are commas within the items.  For example, (a) here, in the middle of the item, there are commas; (b) here there are not; (c) so we use semicolons throughout.

Use commas in exact dates, for example, July15, 2013 (but not in May 2012).