
Originally Posted by
PROESL
They're grammatically correct, but using "reason" and "because" in the same sentence in this manner is redundant.
I would go with one of these. I'd leave out "reason" in the second sentence. It's better simply using because.
Because I had too much to do, my paper was late.
The reason that my paper is later is that I had too much to do.
I left because I was tired.
As for using "because" at the beginning, there's nothing at all wrong with that. The idea that there could be something wrong with it comes from an old schoolmarm prohibition on doing so because the schoolmarms, a subset of the language mavens, were deathly afraid that their sixth graders would write a sentence beginning with "because" and only use the "because" clause, which is a dependent clause and needs to be connected to an independent clause in order to form a complete and grammatically correct sentence in writing. They put a ban on beginning a sentence with "because" because they didn't know how to properly explain that using a dependent clause without connecting it to an independent clause is okay for spoken language but not in writing, unless you use quotations to indicate that it's part of a dialog.