Key Difference:

• “Which” is used in non-defining relative clauses, which give extra information about something but do not define it.
• “That” is used in defining relative clauses, which give essential information needed to understand what we’re talking about.

In non-defining clauses, we never use “that”, only “which”. Let’s explore this further.

Non-Defining Relative Clauses (with “Which”)

A non-defining relative clause adds extra information to a sentence, but it is not necessary to understand the main idea. The sentence would still make sense without the clause.

Example:

• The Eiffel Tower, which is in Paris, is one of the most famous landmarks in the world.

Here, “which is in Paris” gives extra information about the Eiffel Tower, but if we remove it, the sentence still makes sense:

• The Eiffel Tower is one of the most famous landmarks in the world.

Notice the commas around the non-defining clause—this is another key feature!

Defining Relative Clauses (with “That”)

In contrast, defining relative clauses provide information that is essential to the meaning of the sentence. Without it, the sentence would be unclear.

Example:

• The book that I borrowed from the library is fascinating.

Here, “that I borrowed from the library” is necessary to know which book we’re talking about. Without this clause, we wouldn’t know which book is fascinating.

Key Rule:

• Use “which” in non-defining relative clauses (with commas).
• Use “that” in defining relative clauses (no commas).

Varied Examples:

1. Non-Defining with “Which”:
   • My house, which has a red roof, is the oldest on the street. (Extra information, can be removed.)
2. Defining with “That”:
   • The car that I bought last year is very reliable. (Essential information, cannot be removed.)

Common Mistakes:

• ❌ Incorrect: The Eiffel Tower, that is in Paris, is very famous.
  ✅ Correct: The Eiffel Tower, which is in Paris, is very famous.
• ❌ Incorrect: The book which I borrowed is interesting.
  ✅ Correct: The book that I borrowed is interesting.

Practice Time:

Choose which or that to complete the sentences:

1. The museum, ______ has a new exhibition, is worth visiting.
2. The laptop ______ I bought last week is already broken!
3. My friend, ______ loves painting, is organizing an art show.
4. The shoes ______ you recommended are very comfortable.

Answers:

1. The museum, which has a new exhibition, is worth visiting.
2. The laptop that I bought last week is already broken!
3. My friend, which loves painting, is organizing an art show.
4. The shoes that you recommended are very comfortable.

Pro Tip:

Remember: If the clause adds extra, non-essential information, use “which” with commas. If the clause is essential to the meaning, use “that” without commas.