Conjunctions are words such as and, but, so, and if, which are used to connect clauses, sentences, or words. This grammatical superstition arises from the thought that because these words are used to connect separate clauses.The argument against using and or but to introduce a sentence is that such a sentence expresses an incomplete thought (or ‘fragment’) and is therefore incorrect. However, this is a stylistic preference rather than a grammatical rule.