By Marina Pantcheva
Subordinating conjunctions introduce dependent clauses, that is, clauses that cannot express a complete thought on their own. The most common subordinating conjunctions are:
|as||if||till ( or ’til)|
|as if||inasmuch as||unless|
|as long as||in order that||until|
|as much as||lest||when|
|as soon as||now that||whenever|
|as though||provided (that)||where|
(1) The students protested against the decision even though many of them thought it was the right decision to make.
(2) She takes her iPhone with her wherever she goes.
(3) Tom did not eat the sandwich because it was past the expiry date.
Subordinate conjunctions are normally not preceded by a comma, but sometimes a comma can be placed before a subordinate conjunction when separating non-essential parts of the sentence (follow [this link] for more on comma usage).
(4) Tom did not eat the sandwich, which I thought was stupid of him, because it was past the expiry date.