This document discusses the four types of conditional sentences in English. Conditional Type 0 refers to general truths and uses if/when with the present simple. Conditional Type 1 refers to possible future events and uses if/when with the present simple followed by the future simple. Conditional Type 2 refers to unreal present or future situations and uses if with the past simple followed by would, could, or might plus the base verb. The document provides examples of each conditional type and notes the use of were instead of was with the verb to be.