Comma Between Identical or Repeated Words

Use a comma to separate identical words that appear next to each other if they cause confusion or rereading. If an adjective or adverb is repeated for emphasis, use a comma to separate the pair. Also use a comma between non-identical but similar words that could cause misreading. Some common repetitions (e.g., 'that that,' 'had had') are so familiar they do not need a comma. For clarity, a comma between identical words may be necessary even if it separates a subject from its verb.