Inversion involves changing the normal subject-verb order in a sentence. It is commonly used to form questions by placing the verb before the subject. Inversion is also sometimes used when a negative adverb or adverb phrase appears at the start of a sentence, or in conditional sentences with "should", "were", or "had". Inversion can add emphasis or formality. It also follows expressions involving time or place at the start of a sentence, or in sentences beginning with "so + adjective".