The same word may be an adverb, a preposition or a conjunction:
I saw him before. (Adverb)
He stood before me. (Preposition)
He shall do it before I return. (Conjunction)
Compound Conjunctions are groups of words that are sometimes used to do the work of single conjunctions :
Ram as well as Karim went there.
He acted as if (or as though) he were mad.
I shall help you in case you fail.
Conjunctions in pairs
Certain conjunctions are used in pairs; they are sometimes called correlative conjunctioas or correlatives.
Either he or his brother is guilty.
Neither he nor his brother is guilty.
Both he and his brother are guilty.
Not only he but his brother also will go.
Conjunctions are divided into two main classes:
(i) Co-ordinating Conjunctions join words or phrases or clauses of equal rank :
He said this to him and me.
He sat behind you, but in front of me.
You may go; only make no noise.
(ii) Subordinating Conjunctions are those that join a subordinate or dependent clause to a principal clause :
He said that he was ill.
As I am ill, I cannot go.
I shall go if you come.
NOTE:
(a) Clauses are co-ordinate when one is not dependent on another nor enters at all into its construction : I am ill, but he is well. You are healthy and you have got money.
(b) One clause is said to be subordinate to, or dependent on, another when it depends upon the other. The clause on which the subordinate clause depends is called the Principal clause.
(c) Bear in mind that subordinate clauses 100 may be co-ordinate to each other. This is the boy who came here and gave the information. He said that he would come but would not stay.
Co-ordinating Conjunctions are of four kinds
(a) Cumulative or Copulative, that simply add
And : I read and he writes.
Both - and : Both he and his brother will go.
As well as : He as well as his brother will go.
Not only - but also : Not only he but his brother also will go.
Also : He was there, and you also.
(b) Alternative or Disjunctive, denoting a choice between two things
Either - or: either he or his brother will go.
Neither - nor : Neither he nor his brother will go.
Or: Read or you will fail.
Otherwise : Work hard, otherwise you will fail.
(c) Adversative, denoting a contrast between two ideas
But, yet, still : He is poor, but (yet, still he is honest.
However : You are guilty; however, I pardon you this time.
Nevertheless: I am ill; nevertheless, I shall compete.
On the countrary: I do not hate him; on the contrary, I love him.
While, whereas: You failed, while (whereas) your brother passed.
Only : You may come; only make no noise.
(d) Illative, denoting an inference
Therefore, so, consequently: He did not work; therefore (so, consequently) he failed.
For: I do not like him, for he is a wicked boy.
NOTE: For may be regarded as weakened because, and the clause introduced by it may look like a subordinate one. But modern grammarians hold that, as a conjunction, it is co-ordinating. "It introduces a statement by way of explanation as a kind of afterthought .... While a causal clause beginning with since, because, may precede the main sentence, that beginning with for must always follow it."
Subordinating Conjunctions indicate:
(a) Time :
Till, until : Wait till it is night. Wait until I return
After : He came after I had left.
Before : He laid before he could do the work.
When : He came when I was there.
While : Don't go out while it rains.
Since : I have not seen him since I come.
NOTE : The compound conjunctions, as long as, as soon as, so long as fall under this class.
(b) Cause or Reason:
As, since: As (Since) I am ill, I cannot go.
Because : He cannot work because he is ill.
NOTE :
(i) Good English requires that the clause introduced by as, the casual conjunction, should precede the main clause.
(ii) The clause giving the reason in sentences containing expressions reason is", "the reason why" is introduced by that, and not by because or e or on account of :
The reason why he failed is that he did not work hard. The reason of his failure is that he did not work hard. But, the reason of his failure is (not, due to) his idleness.
(c) Purpose :
That, in order that, so that : He works hard that (in order that or so that) he may win the prize.
Lest: I worked hard lest I should fail.
NOTE :
(i) Lest expresses a negative purpose, and should not, therefore, be followed by a negative. Thus, we cannot write "He was afraid lest he should not pass." We must write instead, "He was afraid lest he should fail." It is also to be noted that 'lest is followed by should' or the present subjunctive, never by will or would : Lest we forget; lest he be angry.
(ii) In order that, so that, etc. are followed generally by may or might, in some context, by shall and should, but never by can or could, or could, or will or would:
He encouraged me that (or, in order that) I might not lose heart.
He works hard that (in order that) he may pass.
I give you this advice so that you may succeed.
He is making provision for you so that you may not fall in want.
I give you this advice in order that nothing should be forgotten. (MEU).
(d) Apposition :
That : He wrote to us that he would come.
(e) Condition:
If: I shall go if you come.
Unless: I shall fail unless you help me.
Whether-or-not : I shall go there, whether you like it or not.
Provided : I shall help you provided you obey me.
(f) Effect:
So-that: He worked so hard that he fell ill.
such-that : He is such a fool that I cannot rely on him.
(g) Comparison :
As-as: He is as tall as you.
Than: He is taller than you (are).
So-as : I am not so tall as you (are).
NOTE : Generally, as - as is used in both positive and negative sentences, but
so - as is used in negative sentences.
[But COD has under as 'It is not so (or as) easy as you think.']
(h) Manner :
As - so : As you sow, so shall you reap.
According as : They will be chosen according as they are fit.
AS if, as though:
He behaves as if (or as though) he were (not is) mad (=as he Would have acted if he were mad).
It Looks as if new men had (not have) sprung up.
NOTE :
As as though should invariably be followed by a past conditional, not by a present form (would, not will; could, not can; did not does; was or were, not is; had gone, not has gone; know, not knows).-MEU.
See examples given above. But Wood justifies "He works as if he is drunk".
(i) Concession :
Though (although): Though (although) he is poor, he is honest.
As: Poor as (=though) I am, I am honest.
However : However strong he may be, he cannot do this.
Whoever : Whoever you may be, I cannot allow you here.
Whatever: Whatever you may say, I do not believe you.
