This document discusses conditional sentences and if clauses. It explains that there are three types of conditional sentences: 1) Type one refers to possible and likely conditions with "if" and future tense in the main clause. 2) Type two refers to unlikely or impossible conditions with "if" and "would" in the main clause. 3) Type three refers to unreal past conditions with "if" and "would have" or "should have" in the main clause. It also notes that the if-clause can come before or after the main clause in conditional sentences.