We have seen that the same word may introduce clauses of different kinds. The following examples illustrate this point.

If
He asked if he could go. (Here the subordinate clause ‘if he could go’ is the object of the verb asked. It, therefore, serves as a noun clause.)

If you heat ice it melts. (Here the subordinate clause ‘if you heat ice’ expresses a condition. It, therefore, serves as an adverb clause of condition.)

Who

The man who killed our dog has been arrested. (Here the subordinate clause ‘who killed our dog’ modifies the noun man. It, therefore, serves as an adjective clause.)

I don’t know who he is. (Here the subordinate clause ‘who he is’ acts as the object of the verb know. It, therefore, serves as a noun clause.)

I met John who (= and he) told me the whole story. (Here who acts as a coordinating conjunction.)

That

The connective that serves several purposes. Study the use of that in the subordinate clauses given below.

We eat that we may live.
He worked hard that he might pass.

Here ‘that’ introduces the adverb clause showing purpose. Note that ‘that’ is followed by ‘may’ or ‘might’ in these clauses.

He was so weak that he could not walk.
The coffee was so hot that I could not drink it.
It was so hot that we didn’t go out.

Here ‘that’ introduces the adverb clause showing effect. Note that ‘that’ is preceded by ‘so’ in these clauses.

He is arrogant that he is powerful. (= He is arrogant because he is powerful. Here that introduces the adverb clause of reason.)

He made a promise that he would return soon. (Here the –that clause is used as a complement of the object promise.)

He said that he was going. (Here the –that clause is used as the object of the verb said.)

I remember the story that he told me. (Here the –that clause modifies the noun story. It is, therefore, used as an adjective clause.)

Other connectives which, why, who, as etc., are also used to introduce clauses of different kinds.

Adjective clauses may begin with when, where, why and how when these connectives are preceded by nouns showing time, place, reason and manner respectively.

This is the house where John lives. (Here where introduces the subordinate adjective clause modifying the noun house.)
The reason why she hates me is not known to me. (Here why introduces the subordinate adjective clause modifying the noun reason.)