Possible Duplicate:
Is it really incorrect to start a sentence with “and”?
Is there any valid rule discouraging the use of a certain word to start a sentence?
Usage of “And” in the beginning of a sentence
Can I use "but" at the beginning of a sentence?
I heard that "but, and, so" are not supposed to be used at the beginning of a sentence.
I have noticed, however, a lot of sentences use "but, and, so" as the first word of the sentence.
Are the words at the beginning of the sentence grammatically correct?