What Does That Mean?
That introduces a restrictive (essential) clause, meaning the information is necessary to identify what you are talking about. No commas are used.
That functions as a relative pronoun.
What Does Which Mean?
Which introduces a non-restrictive (non-essential) clause, meaning the information adds extra detail but could be removed without changing the core meaning. Commas are used.
Which functions as a relative pronoun.
That vs Which: Key Differences
| That | Which |
|---|---|
| Essential clause (no commas) | Non-essential clause (with commas) |
| Identifies or restricts the noun | Adds extra information |
| Removing it changes the meaning | Removing it leaves the core meaning intact |
Examples of That in a Sentence
- The car that has a dented bumper is mine.
- Books that are overdue will incur a fine.
- The restaurant that we visited last week is closing.
- She chose the dress that fits best.
Examples of Which in a Sentence
- The car, which has a dented bumper, is parked outside.
- Her novel, which took five years to write, became a bestseller.
- The meeting, which started late, ran until 6 p.m.
- Python, which is free to use, is a popular programming language.
How to Remember the Difference
If you can put the clause in parentheses and the sentence still makes sense, use which with commas. If removing the clause makes the sentence too vague, use that without commas.
Common Mistakes
| Incorrect | Correct | Why |
|---|---|---|
| The house which Jack built is on Elm Street. | The house that Jack built is on Elm Street. | The clause identifies which house, so it is essential. Use 'that.' |
| My car that is blue needs an oil change. | My car, which is blue, needs an oil change. | If you have only one car, the color is extra info. Use 'which' with commas. |
| The books, that are on the shelf, are mine. | The books that are on the shelf are mine. | If you are specifying which books, the clause is essential. Use 'that' without commas. |
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Frequently Asked Questions
Is this rule strict in British English?
British English often uses 'which' for both essential and non-essential clauses. The that/which distinction is more strictly observed in American English.
Can 'that' be omitted?
Yes. In many cases, 'that' can be dropped: 'The book (that) I read was great.' This is called a zero relative pronoun and is common in informal English.
Does this rule apply to people?
No. For people, use 'who' (or 'whom') instead of 'that' or 'which.' 'The teacher who helped me' is preferred over 'the teacher that helped me.'