EXPLANATION The words for, and, nor, but, or, yet and so are coordinating conjunctions; they join sentences and the same sorts of clauses together in the same way that plus and minus signs join elements of mathematical statements together. The word ‘conjunction’ comes from the Latin con and junctio, meaning joining with, so given that conjunctions join things together, it does not make sense to start a sentence with a conjunction.
In the sample error above, ‘or’ has been used to start a new sentence when in fact it is a conjunction and is actually joining (compounding) two simple sentences together to make a compound sentence.
By using conjunctions, you can compound more than two sentences. Take these four simple sentences, for example:
Those four simple sentences can be joined by conjunctions to make this compound sentence:
When we have a list of sentences, we usually replace the conjunctions with commas in all but the final case:
Lightning flashed, thunder roared, rain bucketed down but Dad kept snoring.