Commas to separate two phrases separated by conjunctions

So I was studying for the grammar (English) section of the ACT, and I discovered what seems to be a serious gap in my knowledge. In one particular section, there were 4 questions that I got wrong – all for essentially the same reason.

Examples speak louder than explanation, so:

Q: For centuries, scientists believed in the existence of planets beyond the solar system, but had no way of knowing how common they were or how similar they might be to better-known planets.

The objective of this question was to modify the statement to correct the grammar.


  • No change
  • system. But
  • system but
  • system but they

Now, for me, this question was unambiguously ‘No change;’ however, apparently not – the answer key says that the correct response is ‘system but.’

This was not an isolated occurrence, I realized whilst checking my responses.

Q: The group was originally a four-person ensemble but has expanded to five-part harmonies, a sixth member acts as a sign-language interpreter.

My Ans: ensemble, but has expanded to five-part harmonies…

Correct Ans: ensemble but has expanded to five-part harmonies…


Q: The rings spread over hundreds of thousands of miles, they consist of billions of individual particles that create waves, turbulence and other effects.

My Ans: miles, and consist

Correct Ans: miles, and they consist

This question is slightly different, yes, but my original question still applies. Also note how the author leaves out the Oxford comma – something I would not do.


Q: I would live with a local family, and attend classes at a nearby high school.

My ans: No change

Correct ans: family and attend



Are you an American? Was the test written by a Briton? Examples 1, 2 and 4 are very much the distinction between the BrE and AmE. BrE typically excludes the comma when two independent clauses are conjoined.

As regards the third example, though I don’t suppose it would have been amongst the answer options, also correct, in my opinion, would have been:

The rings spread over hundreds of thousands of miles and consist of
billions of individual particles…

No pronoun or comma.

The answer you cite appears to me to be inconsistent and idiosyncratic. It appears the examiner has a rule that

  • a conjunction is required to join two independent clauses
  • and a comma does not precede this conjunction

but then adds to it

  • unless that conjunction precedes a pronoun referring to the first clause.

Source : Link , Question Author : Equinox , Answer Author : Smartybartfast

Leave a Comment