The document discusses the different types of conditional sentences in English. There are three types: 1) real or likely conditionals which use present or future tense to express conditions that could realistically happen; 2) hypothetical or imaginary conditionals which also use present/future tense but express less likely conditions; and 3) impossible conditionals which use past tense to talk about conditions that did not actually happen. Each type follows specific patterns using conditional clauses and main clauses of different verb tenses. Examples are provided for each conditional type.