The document discusses three types of conditional sentences in English: 1) First conditional uses present tense and refers to possible future events. It uses "if/unless + present" and "will/won't + infinitive". 2) Second conditional uses past tense and refers to imaginary situations. It uses "if/unless + past simple" and "would/wouldn't + infinitive". 3) Third conditional uses past perfect tense and refers to impossible past events. It uses "if/+ past perfect" and "would/wouldn't have + past participle".

1. If Clause 1
If Clause 3
If Clause 2

2. FIRST CONDITIONAL
(POSSIBLE)
If/Unless + Present
simple
Will / won’t + infinitive
If we run, We will catch the bus.
We won’t catch the bus unless we run.

3. SECOND CONDITIONAL
(IMAGINARY)
If/Unless + Past simple would / wouldn’t +
infinitive
If I had time, I would go to yoga clases.
I would go to yoga classes if I had time.

4. THIRD CONDITIONAL
(IMPOSSIBLE)
If/+ Past perfect, would / wouldn’t have+
past participle
If he had tried harder, he would have won.
He would have won if he had tried harder.