Explain the concept of subject-verb inversion.

Subject-verb inversion is a grammatical structure in which the usual order of a sentence, where the subject comes before the verb, is reversed. This inversion occurs when certain adverbial phrases or clauses are placed at the beginning of a sentence for emphasis or to create a specific effect.

Subject-verb inversion is commonly used in various situations, such as in questions, conditional sentences, and certain types of sentences that begin with negative adverbs or adverbial phrases. Let's explore each of these cases in more detail:

1. Questions: In interrogative sentences, the subject and verb are inverted. For example:
- "Are you going to the party?" (Normal order: You are going to the party.)
- "Did she finish her homework?" (Normal order: She finished her homework.)

2. Conditional sentences: In conditional sentences, subject-verb inversion occurs in the if-clause. For example:
- "If I had studied harder, I would have passed the exam." (Normal order: I would have passed the exam if I had studied harder.)

3. Negative adverbs or adverbial phrases: When a sentence begins with a negative adverb or adverbial phrase, subject-verb inversion is used. For example:
- "Never have I seen such a beautiful sunset." (Normal order: I have never seen such a beautiful sunset.)
- "Not only did she win the race, but she also broke the record." (Normal order: She not only won the race, but she also broke the record.)

Subject-verb inversion is also employed in other cases, such as in sentences beginning with "so," "nor," "neither," and "only." These structures are used to add emphasis or to create a specific rhetorical effect. Here are a few examples:
- "So beautiful was the scenery that it took my breath away." (Normal order: The scenery was so beautiful that it took my breath away.)
- "Neither do I want to go nor can I afford it." (Normal order: I neither want to go nor can I afford it.)
- "Only when the sun sets do the stars become visible." (Normal order: The stars become visible only when the sun sets.)

In summary, subject-verb inversion is a grammatical structure that reverses the usual order of a sentence by placing the verb before the subject. It is commonly used in questions, conditional sentences, sentences beginning with negative adverbs or adverbial phrases, and for emphasis or rhetorical effect.