Subordinating conjunctions link phrases or clauses to other clauses. They are called subordinating conjunctions because they transform the clause they introduce into a dependent clause, a clause subordinate to the independent clause in grammatical structure and importance. Some common subordinating conjunctions are after, although, as, as if, as long as, because, before, despite, even if, even though, if, in order that, rather than, since, so that, that, though, unless, until, when, where, whereas, whether, and while.
Even if tighter marketing restrictions and higher excise
taxes prove successful in decreasing tobacco smoking in the U.S., the industry
has a means to counteract loss of revenue: exportation.
--Carl Bartecchi, Thomas MacKenzie, and Robert Shrier, "The Global Tobacco Epidemic," Scientific American
If the subordinating conjunction and its clause precede the independent clause, use a comma to separate the dependant clause from the independent clause. For further discussion of commas with subordinate elements, see Introductory Elements
Although dogged by a few safety problems, the lithium
element has already found its way into some familiar batteries, including those
powering portable computers.
--Sasha Nemecek, "Bettering Batteries," Scientific American
As a general rule, if the subordinating conjunction and associated clause follow the main clause, do not use a comma. An exception occurs when the subordinate clause expresses a contrast, as do clauses beginning with whereas and most clauses beginning with although.
Cutting vehicle mass provides important leverage on efficiency
because it exerts a ripple effect.
--"Improving Automotive Efficiency," Scientific American
Since clauses introduced by a subordinating conjunction are always dependent clauses, they cannot stand alone; they must be linked to independent clauses.
Since the sun and Earth are embedded in the
galaxy. It is difficult for us to obtain an overall view of
the galaxy.
Since the sun and Earth are embedded in the
galaxy, it is difficult for us to obtain an overall view of
the galaxy.
--"The Milky Way," Compton's Encyclopedia
For the ordering of the main clause and subordinate clause and deciding which information belongs in which clause, see Ordering of Phrases and Clauses.
The subordinating conjunction because must be followed by the preposition of when it introduces a noun phrase.
