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Defining vs. Non-Defining and ESL Tips

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Defining vs Non-Defining Clauses: Difference in Meaning

There is a difference in meaning between defining and non-defining clauses that depends on the presence or absence of the comma. For example:

They have two sons who are doctors.

Defining clause; the meaning is that there are more sons in the family, e.g.:

They have two sons who are doctors and one who is an architect.


They have two sons, who are doctors.

Non-defining clause; the meaning is that there are no more sons in the family.

ESL Tips on the Use of Relative Pronouns

Although there is no one single rule to cover all the cases, the following summary may be helpful if you need to make a quick decision:

  1. Use that if the main clause poses the question WHAT? answered by the relative clause;
  2. Do not use that presenting non-essential, additional information (that is, in non-defining relative clauses); use who or which instead;
  3. Use who to refer to people;
  4. Use which to refer to things or to refer to the previous clause as a whole;
  5. If you choose between who or that, use who in writing;
  6. If you choose between which and that, use which in writing;
  7. Do not put a comma before that.