This document summarizes different types of conditional sentences in English including factual, future, present unreal, and past unreal conditionals. It explains the tense and structure of each type of conditional. For example, factual conditionals use the same tense in both clauses, future conditionals use present tense in the if clause and future tense in the result clause, and present and past unreal conditionals use past tense in the if clause and modal verbs in the result clause. The document also discusses alternatives to using "if" such as "unless" and "provided", as well as implied conditions.