Relative Pronouns are used to link parts of sentences together. Common relative pronouns are- who, whom, which, and that.
(Examples of less common relative pronouns are: whomever, whose, whichever, and so forth)
How do you know which one to use in a sentence?
Who and whom always refer to people. Who is always the subject, and whom is always the object. The part of the sentence that starts with ‘whom’ is usually set off by commas. No commas are needed when using ‘who’.
When you find it hard to choose which one to use, test it by trying the following replacements:
Replace “who” in a sentence with the word “he” or “she”, and -
Replace “whom” with “him” or “her.”
To (who / whom) am I speaking?
1. Let's try it with the word "him":
I am speaking to him. - sounds good and uses proper English.
2. Now try it with the word "he":
I am speaking to he. - doesn’t sound right and doesn’t use proper English.
Therefore, because the word "him" sounded correct, we will use "whom" in the original sentence:
To whom am I speaking?
I wanted to speak to (who / whom)?
1. Let's try it with the word "her":
I wanted to speak to her? - done in proper English.
2. Now try it with the word "she":
I wanted to speak to she? - not done in proper English.
Therefore, because the word "her" sounded correct, we will use "whom" in the original sentence:
I wanted to speak to whom?
Which and that always refer to things or objects. The part of a sentence that starts with ‘which’ is set off by commas. No commas are needed when using ‘that’.
"Which" or "that" - Which one to use?
The word ‘that’ is generally used when the information or description following is vital to the meaning or understanding of the sentence. The word “which’ is used when the information or part of the sentence following it can be omitted without seriously changing the meaning of the sentence.
Examples:My bike that we just bought yesterday has a flat tire!
"that we just bought yesterday" is an important part of the sentence. If we take it out, then the entire meaning and feeling of the sentence changes. Therefore, we use ‘that’ instead of ‘which’.
"which is just off Main Street" doesn’t really affect the idea of the school being old. If we take it out then the sentence still means the same thing. Therefore we use ‘which’ instead of ‘that’. We will also use commas to set off that section of the sentence.