English offers many ways to express “because.” Some are wordy and should be avoided due to the fact that they are wordy. (Did you get that? We just made a joke!) Others, like “since” and “as,” need to be used carefully, since you could confuse your readers.
Now let’s be rebellious. Fowler's Modern English Usage points out that the objection to “due to” as a compound preposition is “an entirely 20c phenomenon, but it begins to look as if this use of ‘due to’ will form part of the natural language of the 21c” (4). The American Heritage Guide to Contemporary Usage and Style (5) agrees, stating that “The tide has turned toward accepting ‘due to’ as a full-fledged preposition,” and Garner's Modern English Usage describes such use as "virtually universal" (1).
If you’re a purist, avoid “due to” as a compound preposition, but understand that the majority may soon be against you.
After reviewing the evidence, we say if you’re a purist, avoid “due to” as a compound preposition, but understand that you're in the minority. Whichever way you feel about “due to,” remember that our easy-to-use friend “because” is often standing at attention thinking, "You could use me. Pick me! Pick me!"
Other Times to Use “Due to”
You don’t have to ban “due to” completely. This phrase can mean “payable to” or “supposed to” (6). For example, you could say, “I ask that you pay what is due to me.” Here, you are asking for money that someone owes you. You could also say, “The plane is due to arrive at noon,” meaning the plane should arrive at 12.
“Since” or “Because”?
Strict grammarians may not like it (7), but “since” and “because” can be synonyms (1, 8). “Since I love you, let’s get married” means the same thing as “Because I love you, let’s get married.” (Yes, you can use “because” at the beginning of a sentence.)
Fussy grammarians might be a teensy bit right in some cases, though. The word “since” often refers to how much time has passed, as in “Since yesterday, all I’ve thought about is you.” Sometimes, a sentence with “since” can be interpreted in two ways, and that is when you should avoid using “since” to mean “because.” Take this ambiguous sentence:
“Since they spoke, she’s had second thoughts.” (“Since” could mean “from the time that they spoke” or “because they spoke.”)
A similar problem arises with the word “as,” which can also mean “because,” so keep those little grammarians perched on your shoulder to make sure you don’t write an ambiguous sentence. Granted, it is hard to know when you’re being unintentionally ambiguous. Spend some time away from your writing and then look at it again with fresh eyes, or you could always rope in a friend.