A Conjunction is a word which joins words, phrases or clauses.
*A Conjunction is a word for joining one word to another word, or one sentence to another sentence.—J. C. Nesfield.
*A Conjunction is a word used to joined words or sentences.—Wren & Martin.
Distinction between a Conjunction, a Preposition and Adverb—A Conjunction simply joins words or phrases or clauses. It is never connected with an object as a preposition is, nor does it qualify a word, as an adverb does. The same word may be an adverb, a preposition, or conjunction.
I saw him before (Adverb).
He stood before me (Preposition).
He shall do it before I return (Conjunction).
Compound Conjunctions are group of words that are that are sometimes used to do the work of single conjunctions.
01. Ronaldo as well as Rooney went there.
02. He acted as if (or, as though) he was mad.
03. I will help you in case you fail.
Conjunctions in pairs—Certain conjunctions are used in pairs; they are sometimes called Correlative conjunctions, or Correlatives.
01. Either he or his brother is guilty.
02. Neither he nor his brother is guilty.
03. Both he and his brother are guilty.
04. Not only he but his brother also are guilty.
Conjunctions are divided into two main classes:
(i) Co-ordinate 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) Sub-ordinate or Sub-ordinating Conjunctions are those that join a Sub-ordinate or dependent clause to a principal clause (i. e. a. clause of higher rank).
Examples: He said that he was ill. As I am ill, I cannot go.
Co-ordinate Conjunctions are of four kinds:
(a) Cumulative or Copulative Conjunctions 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.
Or: Read or you will fail.
Not only-but also: Not only he but his brother also will go.
(b) Alternative or Disjunctive Conjunctions denotes 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.
Also: He was there and you also.
(c) Adversative Conjunctions denotes 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 will complete.
On the contrary: 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 Conjunctions denotes 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.
Sub-ordinate Conjunctions indicate:
Till, until: Wait till I am here. Wait until I return.
After: He came after I had left.
Before: He died 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 came.
**Note: The compound conjunctions, as long 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.
That, in order that, so that: He works hard that (In order that or so that) he may win the prize.
Lest: I worked lest I should fail.
That: He said that he was ill.
If: I will go if you come.
Unless: I will fail unless you help me.
Whether-or-not: I will go there whether you like it or not.
Provided: I will help you provided (or provided that) you obey me.
So-that: He works so hard that he fell ill.
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).
Some would confine the use of than as a preposition to relative pronoun only. But the use of the word as a Preposition has come to stay: No one other than him was present there. We elected your son than whom no better man was available. He is better than me in every respect.
**Note: Generally as-as is used in both position 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 will you reap.
According as: They will be rewarded according as they do their duties.
**Note: As if, as though should invariably be followed by a past conditional, and not by a present form. Thus instead of writing—
“He talks as if he is mad.” “it look as if new men have sprung up.” We should write: “He talks if he were mad,” “it looks as if new men had sprung up.”
Though (although): Though (although) he is poor, he is honest.
As: Poor as (although) I am, I am honest.
However: However strong he may be, he cannot lift this weight.