2.What is a Sentence? A sentence is a group of words that you use to communicate your ideas in writing or in speech. (function) It is a complete,independent unit of thought and consists of two main parts:a subject and a predicate (form)2. What is a Sentence? A sentence is a group of words that you use to communicate your ideas in writing or in speech. (function) It is a complete, independent unit of thought and consists of two main parts: a subject and a predicate. (form)