Subordinate or dependent clauses are ones that cannot stand alone. Compare with main or independent clauses, which are clauses that can stand alone. To understand this fully, you need to know the following:

1. A clause is a group of words that contains a subject and a predicate.
2. A subject is the part of the clause indicating what or who performs the action or what the clause is about.
3. A predicate is the part of the clause containing a verb and stating something about the subject.
4. A complex sentence includes a subordinate clause and an independent clause.
5. A subordinate conjunction is a word that begins the subordinate clause and makes that clause weaker than (i.e., reducing the importance of the independent clause).

Now, let’s look at some examples.

Examples

Example 1:

When it rains, it pours.

• This is a complex sentence.
• ‘When it rains’ is the subordinate (or dependent) clause; there is no subject and this is not a sentence. This subordinate clause begins with the word ‘when’ — subordinate clauses  begin with subordinate conjunctions such as when, while, since, and because.
• ‘it pours’ is the independent (or main) clause; the subject is ‘it’ and the predicate is ‘pours’ and this can be a simple sentence on its own.

Example 2:

When it rains, it pours.               vs.                It pours when it rains.

• Note the use of the comma in the first example.
• When the subordinate clause comes first, use a comma at the end of the clause (and not a semi-colon). Note that there are a few exceptions to this general rule; see here for an explanation: http://www.chompchomp.com/terms/subordinateconjunction.htm.
• When the subordinate clause comes last, there is no need for a comma after the independent clause. Again, note the above link for the exceptions to this rule.

Food for Thought

1. Can you think of some other subordinate conjunctions? (check your answers here: http://www.chompchomp.com/terms/subordinateconjunction.htm)
2. Can you think of some categories of subordinators? (see above link)
3. Do you use the comma effectively in your own writing when you have a subordinate clause? Do the exceptions to the rule ever throw you off?
4. Do you prefer to place the subordinate clause at the beginning of a sentence or do you tend to avoid this construction due to confusion over punctuation or as simple preference for word order?