Final answer:
No, a comma does not belong in the sentence 'Since Mitchell Wilson can balance 12 books on his head, his aunt says he has a perfect posture', as there are no nonessential clauses or phrases that require separation by a comma.
Step-by-step explanation:
The sentence in question does not require a comma because the subject 'Mitchell Wilson' is directly followed by the verb 'can balance', and there's no additional information between the subject and the verb that would necessitate a pause. According to common comma errors, a comma should not be placed after a subject unless there's a nonessential clause or phrase that needs to be offset. In this case, the sentence is straightforward and does not include additional clauses that interrupt the flow between the subject and verb.
In the context of commas related to numbers, dates, titles with names, and addresses, commas are used to separate elements for clarity, such as in the given examples. However, when it comes to balancing sentence rhythm with comma usage, we look to carefully constructed writing for guidance. As the passage about the poetic line and breath suggests, commas regulate reading pace and should be used thoughtfully to avoid creating choppy sentences or obscuring meaning.