English teachers sometimes pass along the nonsense they learned from their own teachers. Here are two myths I sometimes hear parroted by my students at my day job:
1. "You can't end a sentence with a preposition."
This is a myth. Certain petrified expressions (i.e., expressions that can be written only one way, with no change in word order) demand that a sentence end with a preposition. A classic example from linguistics:
RIGHT: That's not something I can put up with.
WRONG: That's not something up with which I can put.
Only Mr. Spock might attempt the second locution. Keep that in mind. Only aliens talk this way.
Put up with is a petrified expression. Being petrified, it governs the structure of the part of the sentence in which it appears. You can't shoehorn it into a mythological grammatical schema.
2. "You can't start a sentence with because."
Oh, yeah? Watch me:
Because I love the rebooted Battlestar Galactica, I've left the Presbyterian Church and have become a Caprican polytheist.
I imagine that the "rule" proscribing the use of because at the beginning of a sentence stems from the occurrence of sentence fragments. A teacher will be understandably horrified to see a "sentence" like:
Because it was the right thing to do.
Why is the above wrong? It's not a real fragment, is it? How can it be, when there's an obvious subject (it) and verb (was)?
Keep in mind that because generally functions as a conjunction introducing a subordinate clause (i.e., a subordinating conjunction). If a sentence has a subordinate clause, it's got to have a main clause. Look at these two sentences:
I love you. You've got eleven fingers.
Join them with because:
I love you because you've got eleven fingers.
The main clause is I love you, and the subordinate clause is you've got eleven fingers. The main clause can stand alone as an independent clause; a subordinate clause, by contrast, never stands alone. And that, ladies and gentlemen, is why a stranded subordinate clause beginning with because is, for all intents and purposes, a fragment.
Keep this in mind as well: it's fine to stick because at the beginning of a sentence since you can reverse the order of the clauses and preserve the sentence's meaning. To wit:
I love you because you've got eleven fingers. (is the same as)
Because you've got eleven fingers, I love you.
Watch out for those language myths. Learn how to look up grammar and usage points yourself by consulting authoritative resources both in the library and online.