help using who or whom

The person who I called is my sister.

For whom is this letter?

Whom will we select?

Who told us about Frank?

Whom did he call?

Who sat next to me?

1. is wrong.

Understanding the correct usage of "who" and "whom" can help you express yourself more accurately in formal writing or conversations. Here's how you can determine whether to use "who" or "whom" in each of the given sentences:

1. The person who I called is my sister.
To determine whether to use "who" or "whom" in a sentence, you can rephrase the sentence and answer the question using personal pronouns. Here, you can rephrase the sentence to "I called her." Since "her" is used instead of "she," "who" is the correct choice. Therefore, the correct sentence is: "The person who I called is my sister."

2. For whom is this letter?
Once again, you can rephrase the sentence and answer the question using personal pronouns. Here, you can rephrase the question to "This letter is for him." Since "him" is used instead of "he," "whom" is the correct choice. Therefore, the correct sentence is: "For whom is this letter?"

3. Whom will we select?
Rephrasing the question to "We will select him" indicates that "whom" is correct. Therefore, the correct sentence is: "Whom will we select?"

4. Who told us about Frank?
Rephrasing the question to "He told us about Frank" indicates that "who" is correct. Therefore, the correct sentence is: "Who told us about Frank?"

5. Whom did he call?
Rephrasing the question to "He called him" indicates that "whom" is correct. Therefore, the correct sentence is: "Whom did he call?"

6. Who sat next to me?
Rephrasing the question to "She sat next to me" indicates that "who" is correct. Therefore, the correct sentence is: "Who sat next to me?"

Remember, "who" is used in the subject position (doing the action), whereas "whom" is used in the object position (receiving the action).