This document discusses different types of conditional sentences in English:
- Zero conditional sentences use the present tense to describe general truths.
- First conditional sentences use the present tense and future tense to describe probable events.
- Second conditional sentences use the past tense and modal verbs like "would" to describe improbable or hypothetical events.
- Third conditional sentences use the past perfect tense and modal verbs like "would have" to describe events that did not happen in the past.
- Other conditional structures like "unless", "provided", and "wish" clauses are also explained. Examples are provided to illustrate the different conditional sentence types.