Grammatically Correct: The writer's essential guide to punctuation ...

GRAMMATICALLY CORRECT
STARTING A SENTENCE WITH A CONJUNCTION
And just what's so wrong with starting a sentence with a conjunction,
anyway? A conjunction is a word that defines the relationship (forms
the junction) between discrete units of thought: He bought a crate
of bananas and proceeded to hurl them at passing trains; The
article annoyed me so I used it to line the birdcage; Patsy brushed
up on her iridology skills, but Samantha insisted on visiting
the aromatherapist; Geoffrey couldn't decide jf he should go to
dentistry school or become a juggler. Such words normally go
within a sentence rather than at its beginning, since they act to link
one element to another.
Writers are often taught that certain conjunctions should never
be put at the start of a sentence, since doing so would create a
sentence fragment. (For the definition of a grammatically complete
sentence, see "Basic Sentence Structure" on page 55.) In some
cases, a fragment would undeniably be the result:
There were no rugs on the floor. Or curtains at the windows.
Try to catch me. If you can.
A sentence fragment is not illegal per se, though: Just because
it isn't a grammatically complete unit doesn't mean it can't communicate
clearly and effectively. Experienced writers may deliberately
use the occasional sentence fragment for emphasis or to capture a
particular flavor. Provided that this is done only sparingly and that
it is justified by the context, the strategy may be effective. (Note,
though, that a dash can also be used for emphasis, and should be
considered preferable if the effect would be the same. For a description
of this use of the dash, turn to page 157.)
And in many cases-such as this sentence-opening with a conjunction
does not turn a sentence into something grammatically
incomplete; it simply serves to connect the current information
more strongly to the information or ideas that come before it. The
conjunctions and, but and however in particular may be used to
good effect this way, and sometimes will be the most forceful, concise
and unambiguous means of expressing the relationship between a
sentence and its predecessor.
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