No Comma in a Compound Dependent Construction
The Comma
Rulebase Summary
When a coordinate conjunction (and, but, or, nor) joins elements that cannot stand alone as complete sentences — such as two verbs sharing the same subject, two prepositional phrases, two dependent clauses, or two completer words — do not use a comma before the conjunction. A comma before the conjunction is only correct when both sides are independent clauses (each with its own subject and verb forming a complete thought).
Examples
A. The firm foreclosed, but did not find a new buyer for the property.
A. The firm foreclosed but did not find a new buyer for the property.
Two verbs sharing one subject — no comma before 'but'.
A. You can find it across the street, and down the block.
A. You can find it across the street and down the block.
Two prepositional phrases joined by 'and' — no comma.
Transcript Notes
In spoken language, compound dependent clauses sometimes drop the introductory word in the second or third clause. Since the conjunction cannot link grammatically unequal elements, the missing introductory word signals these are dependent clauses in compound construction, and no comma goes before the conjunction.
Style Guide References (1)
BGGP