Coordinating conjunctions join words, phrases, or clauses of equal grammatical rank. "And" adds information ("apples and oranges"), "or" presents alternatives ("tea or coffee"), and "but" introduces contrast ("small but powerful"). These three small words appear with remarkable frequency because they allow speakers and writers to combine ideas smoothly and efficiently.
Subordinating conjunctions connect a dependent clause to a main clause, expressing specific relationships. "If" introduces a condition, as in "If it rains, we will stay inside." "Because" gives a reason or cause, as in "We stayed inside because it rained." "That" can introduce noun clauses ("I know that you are right") or relative clauses ("the book that I read"). "So" can act as a coordinating conjunction meaning "therefore" ("It was cold, so we stayed inside") or as an adverb of degree ("so tired").
Adverbial conjunctions often answer questions about time, place, reason, or manner. "When" asks about time, "where" asks about place, "why" asks about reason or purpose, and "how" asks about manner or means. These four words form many common question patterns: "When did you arrive?" "Where are we going?" "Why did you say that?" "How does this work?" Together with "who," "what," and "which," they make up the core of English question words.