What is the study of how sentences are formed and the rules of grammar?

The study of how sentences are formed and the rules of grammar is known as syntax. Syntax involves the arrangement of words and phrases to create well-formed sentences in a language. It encompasses understanding how different parts of speech (such as nouns, verbs, adjectives, etc.) interact and govern each other within sentences.

This study is crucial for both native speakers and language learners, as it provides a framework for constructing grammatically correct sentences and understanding sentence structure. By analyzing syntax, learners can improve their skills in composing written and spoken language effectively, enhancing their overall communication abilities.

The other options refer to different aspects of linguistic study: phonetics focuses on the sounds of speech, discourse analysis examines the structure of written or spoken communication beyond the sentence level, and graphemics involves the study of writing systems and their symbols. These areas, while important, do not address the formation and grammatical structure of sentences in the same way that syntax does.