This document discusses the importance and forms of conditional sentences. There are four types of conditional sentences: Conditional-0 uses simple present tense; Conditional-1 uses simple present followed by future tense; Conditional-2 uses simple past followed by "would"; Conditional-3 uses past perfect followed by "would have" plus the past participle. Conditionals are important as they help express things that may happen and take many forms to give advice, express regret, or discuss facts.