Question 122·Medium·Boundaries
Ancient astronomers could predict planetary alignments with remarkable _____ they lacked the instruments needed to explain why those alignments occurred.
Which choice completes the text so that it conforms to the conventions of Standard English?
For boundaries questions, first decide whether you have two independent clauses. If you do and you’re using a coordinating conjunction (FANBOYS) to connect them, use a comma before the conjunction and avoid adding extra commas around it.
Hints
Check for complete clauses
After inserting an option, see whether the words before and after the joining word can each stand alone as a complete sentence.
Consider the relationship
The second clause contrasts with the first. Look for a coordinating conjunction that commonly signals contrast.
Remember the comma + FANBOYS pattern
When a FANBOYS conjunction connects two independent clauses, put a comma right before the conjunction.
Check for unnecessary commas
If there is a comma immediately after the conjunction, ask whether the conjunction is being (incorrectly) treated like a parenthetical interruption.
Step-by-step Explanation
Identify the clause structure
With any option inserted, the text before "but" ("Ancient astronomers could predict planetary alignments with remarkable accuracy") is an independent clause, and the text after "but" ("they lacked the instruments needed to explain why those alignments occurred") is also an independent clause.
Determine the relationship
The second clause contrasts with the first (successful prediction vs. lack of explanatory instruments), so a contrasting coordinating conjunction fits the meaning.
Apply the FANBOYS punctuation rule
When a coordinating conjunction (FANBOYS) joins two independent clauses, the standard pattern is:
independent clause, conjunction independent clause
So you need a comma immediately before "but," and you should not add an extra comma right after "but".
Eliminate choices and select the answer
- "accuracy but" → missing the required comma before a coordinating conjunction joining two independent clauses.
- "accuracy, but" → correct: comma before "but," and the second independent clause follows.
- "accuracy; but" → incorrect: a semicolon should not be used directly before a coordinating conjunction like "but."
- "accuracy, but," → incorrectly adds a comma after the coordinating conjunction.
Therefore, the correct choice is accuracy, but.