The restrictive and non-restrictive clauses are two types of adjective clauses.  An adjective clause is a clause that acts as an adjective (i.e. modifies noun) in a sentence.

Example: I saw a kid who was crying.                     

The clause ‘who was crying’ is an adjective clause because it modifies (gives information about) the noun ‘kid’ in the sentence. Hence, as restrictive and non restrictive clauses are two types of adjective clauses, they also modify (give information about) a noun in a sentence.

A restrictive clause modifies a noun by giving information about it as well as by specifying it. On the other hand, a nonrestrictive clause modifies a noun only by giving information about it but does not specify it.

Read the following example for a better understanding:

My friend who has red hairs won the competition.       (Restrictive Clause)
My friend, who has red hair, won the completion.          (Nonrestrictive Clause)

In the first sentence, the clause ‘who has red hair’ is written without commas. It is a restrictive clause. It gives information (having red hair) about the friend who won the competition. It also specifies the friend. It means that I have only one friend who has red hair and that friend won the competition.

In the second sentence, the clause ‘who has red hair’ is written with commas. It is a nonrestrictive clause. It gives information (having red hair) about the friend, but it does not specify the friend. It means that I have many friends who have red hair; and it can be any friend among those friends (having red hair) who won the competition.

The difference between restrictive and nonrestrictive clause lies in the interpretation of a sentence. If a clause is written without commas, its writer intends to specify the noun (restrictive clause). If a clause is written with commas, its writer intends not to specify the noun.

Example:

The man who is wearing a white shirt is my father.            (CORRECT)
The man, who is wearing a white shirt, is my father.          (WRONG)

In the above sentence, the clause refers to a specific person ‘father’. Hence, the writer cannot use a nonrestrictive clause. Because there can be many men wearing white shirts. But the writer points to only one person who is his father. Therefore, this clause will be written without commas to make it a restrictive clause and to refer to a single person ‘father’.

Restrictive Clause	Non-restrictive Clause
Restrictive Clause is also called Essential Clause. Restrictive Clause must not be set off by commas in a sentence. As it is used to specify the noun, it is essential to the meaning of the sentence. If it is taken out of a sentence, the meaning of the sentence would be affected. It does not only give additional information but also identifies the noun.	Non-restrictive Clause is also called Non-essential Clause. Non-restrictive Clause must be set off by commas in a sentence. As it does not specify the noun, it is not essential to the meaning of sentence. Even if it is taken out of the sentence, the meaning of the sentence would not be affected. It gives only additional information about the noun but without specifying the noun.

 

• ‘That’ is used to start a restrictive clause.
• ‘Which’ is used to start a nonrestrictive clause.

Examples:
The table that is made of wood is beautiful.                        (Restrictive Clause)
A table, which is made of wood, is beautiful.                       (Nonrestrictive Clause)

This means the usage of the word ‘that’ or ‘which’ with a clause would turn it into either a restrictive or a nonrestrictive clause. In other words, a clause starting with the word ‘that’ or ‘which’ would be interpreted differently. For instance, a clause starting with the word ‘that’ not only gives more information about the noun but also specifies it. However, a clause starting with the word ‘which’ gives more information about the noun but does not necessarily specify the noun.