A colleague was wondering whether, in something such as the title of this post, the b in because should be lower-cased, since Because it’s a complete sentence isn’t a complete sentence.
Of course, lower-casing the b wouldn’t result in the formation of a more complete sentence, and it would make a difference in how it could be read – a lower-cased follow-on after a question tends to imply that what follows is an explanation or addendum to the question, whereas a capital tends to indicate a response. But the important point I want to make today is that Because it’s a complete sentence actually is a complete sentence.
A complete sentence has a subject (sometimes implied) and a predicate. In this sentence, it is the subject and is a complete sentence is the predicate. Nor is there in reality a rule that a sentence can’t begin with a conjunction; that’s actually just a superstition invented a couple of centuries ago by people who didn’t understand what they were talking about (notably one Robert Lowth, who vandalized English teaching quite badly in 1762 with a book of inane invented superstitions that caught on). It was no problem for Shakespeare or the translators of the King James Bible, among other true standard-setters.
But the sense of the sentence is incomplete, one may protest! It requires something to have come before! Um, so? We have no issue with beginning sentences with other discourse markers that relate them to previous sentences (However, it’s a complete sentence – no one calls that incomplete, but you couldn’t start an essay with it; it requires a preceding sentence), and we have no issue with such things as pronouns that refer to entities in other sentences (most of the times we use he, she, or it we are referring to an entity established in a different sentence, so the sentence is not self-sufficient). The fact that a sentence in isolation is semantically incomplete does not make it syntactically invalid.
(It occurs to me that a church can be quite a good place to let opening conjunctions pass unremarked, even at the very start of a passage. A famous hymn begins “And can it be that I should gain an interest in my saviour’s blood?” A common Christmas reading from the Bible starts “And in that country there were shepherds.”)
Meanwhile, no one seems to have qualms about Why? even though it is clearly less complete than the sentence that followed.
It’s true that certain registers (tones, contexts, levels of use) tend to exclude the use of conjunctions at the start of sentences; this is because someone made up that “rule” and the people who established those registers tended to adhere to it. But registers also shift over time in what they allow, and even formal writing is gradually coming back to match ordinary English – and the English of Shakespeare and other greats – in this respect.