The document discusses different types of conditionals in English. It describes zero, first, second, and third conditionals. The zero conditional uses the simple present tense in both parts of the sentence to describe events that always happen under certain circumstances. The first conditional uses the present tense followed by the future tense to talk about possible future events. The second conditional uses the past tense followed by the modal "would" to describe hypothetical or unlikely situations. The third conditional uses the past perfect tense followed by "would have" to talk about hypothetical past events that did not actually happen.