Sorting out the confusion.
The grammar authorities are going to battle it out today. For they all have a different opinion about our topics: the merits of using the word “for” to mean “because,” and whether it’s OK to start a sentence with the word “for.”
Now, guest-writer Bonnie Trenga writes,
The experts' opinions range from,
yes, go ahead and put a “for” wherever you like—in the middle or at the beginning of a sentence; to
yes, but “for” belongs best at the beginning of an independent clause; to
no, no way—you’re not allowed to put “for” at the beginning of a sentence.
Yikes! Who’s right? You’re going to upset someone no matter what you do.
Using “For” in the Middle of a Sentence
The experts do agree that you can use the word “for” as a conjunction to mean “because” or “since.” In fact, it's been used that way for more than a thousand years (1). No doubt you’ll come across sentences like
I was tired after my journey, for I had been forced to bike 20 miles.
You could just as easily use the word “because” instead of “for.” No grammarian would gripe about either sentence.
When you do use “for” in the middle of a sentence in that manner, one authority (2) suggests you use punctuation—in our example sentence a comma—before your “for.”
I was tired after my journey, [comm for I had been forced to bike 20 miles.