Method

1. Find out all the finite verbs in the sentence. Remember that there are as many clauses as there are finite verbs.
2. Find out the principal clause
3. Find out the subordinate clause or clauses
4. Determine what function each subordinate clause serves and identify it as a noun clause, adjective clause or adverb clause.
5. Show how each subordinate clause is related to the principal clause.
6. Analyze the principal clause and subordinate clauses separately.

Study the following examples carefully.

I warned him that he would be dismissed.

The sentence given above has two clauses because it has two finite verbs – warned and would be dismissed.
Upon closer examination it is easy to find that the clause ‘I warned him’ can stand by itself because it makes complete sense. A clause which makes complete sense and can stand by itself is called a main or principal clause. Now consider the clause ‘that he would be promoted’. It has a subject (he) and a predicate of its own (would be promoted), but it doesn’t make complete sense. It is therefore a subordinate clause.

Once you have found out the principal clause and the subordinate clause, you have to determine what function each clause serves in the sentence. Here the subordinate clause ‘that he would be promoted’ acts as the direct object of the verb ‘warned’.

We have seen that the object of a verb will always be a noun or its equivalent. And since the clause ‘that he would be promoted’ acts as the object of a verb it is a noun clause by nature.

More examples are given below:

Unless he apologizes he will be punished.

Principal clause: He will be punished
Subordinate clause: Unless he apologizes

Here the subordinate clause ‘unless he apologizes’ modifies the verb ‘punished’ by expressing a condition. It, therefore, serves as an adverb clause of condition.

When the siren sounded, all traffic came to a stop.

Principal clause: All traffic came to a stop
Subordinate clause: When the siren sounded

Here the subordinate clause ‘when the siren sounded’ modifies the verb came by saying when the action took place. It, therefore, serves as an adverb clause of time.

More examples are given below:
It was Commander Peary who discovered that Greenland itself was an island.

The sentence given above consists of three clauses because it has three finite verbs – was, discovered and was.

Principal clause: It was Commander Peary
First subordinate clause: who discovered
Second subordinate clause: that Greenland itself was an island

Here the subordinate clause ‘who discovered’ modifies the noun Commander Peary. It, therefore, serves as an adjective clause. The second subordinate clause ‘that Greenland itself was an island’ is the object of the verb ‘discovered’. It, therefore, serves as a noun clause.