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Feature Simple Sentence Compound Sentence Complex Sentence
Number of Ideas One complete idea. Two complete ideas. One main idea + one extra (dependent) idea.
Number of Verbs Usually one main verb. Two main verbs (one for each idea). Two verbs (one for the main idea, one for the extra idea).
Conjunctions Can use conjunctions (like "and" for lists), but not required. Must use a conjunction (like FANBOYS: for, and, nor, but, or, yet, so). Uses special conjunctions (like because, if, when, although) for the extra idea.
Examples with Conjunctions "I like cats and dogs." (One verb: "like," joining a list.) "I like cats, and she likes dogs." (Two verbs: "like" and "likes.") "I like cats because she likes dogs." (Main: "like," Extra: "likes.")
Subject One subject doing the action. Two subjects (can be same or different). One main subject, plus an extra subject in the dependent part.
Can Stand Alone? Yes, it’s complete by itself. Each part could stand alone as a separate sentence. Main idea can stand alone; extra idea cannot.
Comma Use No comma needed before conjunction (if used). Comma usually comes before the conjunction. Comma depends: often after the extra idea if it comes first (e.g., "Because I’m tired, I sleep.").
Example "I run and jump." (One idea, verbs "run" and "jump" as a list.) "I run, but she jumps." (Two ideas, verbs "run" and "jumps.") "I run because she jumps." (Main: "I run," Extra: "because she jumps.")

No sentence can start with because because because is a ....