When do you use a comma?
Use a comma
between elements (including before and and or) in a series of three or more items.
- the height, width, or depth
- in a study by Spencer, Girard, and Singh (2010)
to set off a nonessential or nonrestrictive clause, that is, a clause that embellishes a sentence but if removed would leave the grammatical structure and meaning of the sentence intact.
- Switch A, which was on a panel, controlled the recording device.
to separate two independent clauses joined by a conjunction.
- Cedar shavings covered the floor, and paper was available for shredding.
to set off the year in exact dates.
- April 25, 2011, was the correct date.
- April 2011 was the correct month.
to set off the year in parenthetical reference citations
- (Harper, 2012)
- (Nguyen, 2009, demonstrated....)
to separate groups of three digits in most numbers of 1,000 or more
Do not use a comma
before an essential or restrictive clause, that is, a clause that limits or defines the material it modifies. Removal of such a clause from the sentence would alter the intended meaning.
- The switch that stops the recording device also controls the light.
between two parts of a compound predicate
- The results contradicted Smith's hypothesis and indicated that the effect was nonsignificant.
to separate parts of measurement
- 8 years 2 months
- 3 min 40 s
(adapted from the sixth edition of the APA Publication Manual, © 2010)