Analysis of a Clause
The same word may introduce clauses of different kinds. It is therefore wrong to judge a clause from the word which introduces it. The exact nature of each clause should be figured out from the kind of function it serves in the sentence.
I don’t know when he will arrive. (Here the subordinate clause ‘when he will arrive’ is the object of the verb know. It, therefore, serves as a noun clause.)
Tell me the time when you intend to return. (Here the subordinate clause ‘when you intend to return’ modifies the noun time. It is therefore used as an adjective clause.)
When the cat is away the mice play. (Here the subordinate clause ‘when the cat is away’ acts as an adverb clause of time modifying the verb play.)
There are as many clauses in a sentence as there are finite verbs. Note that infinitives, participles and gerunds are not finite verbs.
For and because
For is a coordinating conjunction. It is used to introduce a coordinate clause. Because is a subordinating conjunction. It is used to introduce a subordinate clause.
He did not go out, for it was raining. (Here the coordinating conjunction for joins two main clauses ‘he did not go out’ and ‘it was raining’.)
He did not go out because it was raining. (Here the subordinating conjunction because joins the principal clause (he did not go out) with the subordinate clause (it was raining).)
In an indirect question whether introduces a noun clause.
I don’t know whether he would come. (Here the clause introduced by whether acts as the object of the verb know. It is therefore a noun clause.)
In conditional sentences whether introduces an adverb clause of condition. It is usually followed by or.
You are going to do that job whether you like it or not. (Here whether introduces the adverb clause of condition whether you like it or not.)
A sentence put inside inverted commas is always a noun clause.
Indirect questions introduced by if or whether are noun clauses.
He asked me whether I liked the idea. (Here the indirect question ‘whether I liked the question’ acts as the object of the verb asked.)
When, unless, if, till etc
After the conjunctions when, unless, if, till, whether…or, while and though, the predicate verb ‘to be’ is often understood and not expressed.
I broke my leg while getting down the ladder. (= I broke my leg while I was getting down the ladder.)