When is it wrong to 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)