از گرامرلی که دیگه نمیشه اشتباه گرفت ;)
من توضیح فارسی خودم رو میدم، ولی توضیحات دو سایت انگلیسی [که یکیشون از گرامرلی هست] رو هم می‌ذارم.
شما زمانی دوطرف بدل (appositive) کاما می‌ذاری که nonrestrictive باشه. یعنی بود و نبودش لطمه‌ای به جمله نزنه، یعنی داره برای روشن‌تر شدن موضوع یه اطلاعاتی رو میده، اگه از جمله حذف بشه، تأثیری روی معنای کلی جمله نداره. حالا چرا نمیشه تو این مثال کاما گذاشت؟
چون اگه کاما بذاریم، یعنی Stephen یه دادۀ اضافی هست و اگه حذفش کنیم، معنای جمله تغییر نمی‌کنه. خب حالا Stephen رو حذف کنی تهش چی می‌مونه؟
Alec Baldwin’s brother is the most underrated Baldwin
خب حالا سؤال پیش میاد، از کجا بدونیم منظور نویسنده کدوم برادر الک بالدوین بوده. پس این یعنی به معنای جمله لطمه زده.
توضیح خود سایت گرامرلی:
When an appositive noun or noun phrase contains an essential element without which a sentence’s meaning would materially alter, do not frame it with commas.
My friend, Bill, owes me fifty dollars. Incorrect
My friend Bill owes me fifty dollars. Correct
و بعد این توضیح هم نوشته، فقط در یک صورت جملۀ اول می‌تونه درست باشه اون هم زمانی که طرف فقط یه دونه دوست داشته باشه و بقیه بدونن که منظورش از «دوستم» کدوم دوستش هست.
Rule: When an appositive is essential to the meaning of the noun it belongs to, don’t use commas. When the noun preceding the appositive provides sufficient identification on its own, use commas around the appositive.
Example: Jorge Torres, our senator, was born in California.
Explanation: Our senator is an appositive of the proper noun Jorge Torres. Our senator is surrounded by commas because Jorge Torres is a precise identifier.
Example: Our pediatrician, André Wilson, was born in California.
Explanation: Our pediatrician is still a relatively precise identifier so André Wilson is not considered essential.
Example: CEO Julie Minsky will be our featured speaker.
Explanation: Julie Minsky is necessary to help identify CEO, so no commas are used.
Example: Julie Minsky, CEO, will be our featured speaker.
Explanation: Julie Minsky is a precise identifier so the appositive is surrounded by commas.
Example: The girl who received a scholarship is my sister.
Explanation: The girl by itself is not sufficient information.
Example: My sister, who received a scholarship, will attend Harvard.
Explanation: My sister is a relatively precise identifier.
Example: My friend Harvey is an animal lover.
Explanation: My friend is not a precise identifier because one may have numerous friends.
Example: Harvey, my friend, loves animals.
Explanation: Harvey is a precise identifier.
https://www.grammarbook.com/blog/commas/commas-with-appositives/
app chiMigan اپ چی میگن
