The document discusses conditional tenses and conditional sentences. There are two types of conditional tenses: present conditional tense formed with would/should + infinitive, and perfect conditional tense formed with would/should + perfect infinitive. There are three types of conditional sentences. Type I uses present tense in if clause and future in main clause. Type II uses past tense in if clause and conditional tense in main clause. Type III uses past perfect in if clause and perfect conditional in main clause. The document concludes with exercises to practice the different conditional sentences.