Comma Before Conjunction Linking Two Command-Form Sentences
The Comma
Rulebase Summary
When a coordinate conjunction links two sentences that both use the command form — where the subject 'you' is assumed — use a comma before the conjunction. If both command sentences are short, the comma may be omitted. Some experts believe the assumed 'you' applies only to the first verb and that the conjunction simply links two verbs, making the comma unnecessary. As always, be consistent.
BGGP Separating Comma.4 · p.172
Examples
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Q. Look at the document and tell me what you see.
✓
Q. Look at the document, and tell me what you see.
Two command-form clauses with assumed 'you' — comma before the conjunction.
✓
Q. Sit down and be quiet.
Both commands are short — comma may be omitted.
Style Guide References (1)
BGGP
Separating Comma.4
Page 172