+329.+ Conjunctions are divided into classes, as are other parts of
speech, according to the work which they do. Notice the following
sentences and notice how the use of a different conjunction changes the
meaning of the sentence.
We are united _and_ we shall win.
_When_ we are united, we shall win.
In the first sentence the conjunction _and_ connects the two clauses,
_we are united_ and _we shall win_. They are both independent clauses,
neither is dependent upon the other, and both are of equal importance.
But by the use of the conjunction _when_, instead of the conjunction
_and_, we have changed the meaning of the sentence. There is quite a
difference in saying, _We are united and we shall win_, and _When we are
united we shall win_.
By connecting these two statements with the conjunction _when_, we have
made of the clause, _we are united_, a dependent clause, it modifies the
verb phrase _shall win_. It tells _when_ we shall win, just as much as
if we had used an _adverb_ to modify the verb phrase, and had said, _We
shall win tomorrow_, instead of, _We shall win when we are united_.
So in these two sentences we have two different kinds of conjunctions,
the conjunction _and_, which connects clauses of equal rank or order,
and the conjunction _when_, which connects a dependent clause to the
principal clause.
+330.+ So the conjunctions like _and_ are called co-ordinate
conjunctions. _Co-ordinate_ means literally of equal rank or order.
Conjunctions like _when_ are called sub-ordinate conjunctions.
_Sub-ordinate_ means of inferior rank or order.
So we have our definitions:
+331.+ +A conjunction is a word that connects words or phrases or
clauses.+
+A co-ordinate conjunction is one that joins words, phrases or clauses
having the same rank.+
+A subordinate conjunction is one that connects a dependent clause to
the principal clause.+