Zero Condition:

the situation is real and possible, general truths.

simple present.

If this thing happens, that thing happens.

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TYPE 1 CONDITIONAL

used to refer to the present or future where the situation is real.

simple present, and the main clause is in the simple future.

If this thing happens,that thing will happen.

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TYPE 2 CONDITIONAL

a time that is now or any time, and a situation that is unreal.

Not based on fact. and ahypothetical condition and its probable result.

If this thing happened, that thing would happen. (but I'm not sure this thing will happen) OR

that thing would be happening.

"If I were taller, I would buy this dress."

"If you really loved me, you would buy me a diamond ring."

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TYPE 3 CONDITIONAL

used to refer to a time that is in the past, and a situation that is contrary to reality.

it is used to refer to an unreal past condition and its probable past result.

If this thing had happened, that thing would have happened. (but neither of those things really happened) OR

that thing would have been happening.

hypothetical and unreal, because it is now too late for the condition or its result to exist.

"If you had studied harder,you would have passed the exam."

"I would have believed you if you hadn't lied to me before."

If I had worked harder I would have passed the exam. (But I didn't work hard, and I didn't pass the exam.)

If I had known you were coming I would have baked a cake. (But I didn't know and I didn't bake a cake.)

I would have been happy if you had called me on my birthday. (But you didn't call me and I am not happy.)

I would have bought you a present if I had known it was your birthday.

: use modals in the main clause instead of "would" to express the degree of certainty, permission

If I had worked harder I might have passed the exam.

You could have been on time if you had caught the bus.

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MIXED TYPE CONDITIONAL

used to refer to a time that is in the past, and a situation that is ongoing into the present.

The mixed type conditional is used to refer to an unreal past condition and its probable result in the present.

'if' clause is the past perfect, and the tense in the main clause is the present conditional.

*the time is the past in the "if" clause and in the present in the main clause.

If this thing had happened that thing would happen.

If this thing had happened that thing would happen. (but this thing didn't happen so that thing isn't happening)

If I had worked harder at school I would have a better job now.

If I had studied I would have my driving license. (but I didn't study and now I don't have my license)

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Second type of mixed conditional :

If this thing happened that thing would have happened.

"If I wasn't afraid of spiders, I would have picked it up."