Comma Between Identical Repeating Words
The Comma
Rulebase Summary
Use a comma to separate two identical words that appear next to each other and serve exactly the same grammatical function. This does not apply when the two identical words serve different functions — for example, when one is a relative pronoun and the other is demonstrative, or when one is an auxiliary verb and the other is the main verb. When repeated words create a double-verb situation, a comma between them is optional — use your judgment based on readability.
Examples
Q. Whatever it is is a concern to us all.
Q. Whatever it is, is a concern to us all.
Comma between identical words serving the same function aids readability.
A. All that was left was left to her sister.
A. All that was left, was left to her sister.
Optional comma for clarity when a repeated word creates a double-verb situation.
Transcript Notes
Repeated words that create a double verb (where the same word appears as an auxiliary and then as a main verb) may or may not need a comma. The comma could separate the subject from the verb, which is normally not done. However, a comma may be necessary for clarity and ease of reading. Use judgment about whether the comma helps the reader.
Style Guide References (1)
BGGP