This document discusses the key elements of sentences including: 1. Sentences tell a complete thought and include a subject and predicate. There are four types of sentences - declarative, interrogative, imperative, and exclamatory - distinguished by their ending punctuation. 2. A subject names who or what the sentence is about, and can be single or compound. A predicate tells what the subject does or is, and is always a verb which can also be single or compound. 3. Compound sentences join two independent clauses with a comma and conjunction. Compound subjects and predicates combine elements while keeping the same predicate or subject.