Notice that a restrictive, or necessary, clause is not separated from the rest of the sentence by commas.
Who and which are sometimes used with restrictive force; as,
1. Those who have finished their work may leave. (Not everybody.)
2. Have you read the book which he recommended? (He recommended but one.)
Interrogative pronouns are used in asking questions. They are who, which, what. Who refers to persons; which refers to persons or things, and is used to distinguish one object from another; what refers to things. They are declined as follows:
Singular and Plural
| Nom. | who | which | what |
| Poss. | whose | (of which) | (of what) |
| Obj. | whom | which | what |
The interrogative pronouns which and what are frequently used as adjectives. In this case they are called pronominal adjectives. Compare:
| Pronoun: Which of these hats do you prefer? |
| Adjective: Which hat do you prefer? |
The demonstrative pronouns are this and that with their plurals these and those. They are always used to point out, or demonstrate, the noun to which they refer. This and these are used for objects near at hand, or recently named; that and those are used for objects far away, or not recently named.