1.   Future  possible

เหตุการณ์สามารถเป็นไปได้ในอนาคต

Structure

If + v  ( Present ) , subj +  will

+ infinitive หรือ  - subj + will
+ infinitive , + if + V (Present)
ถ้ามี should ให้ขึ้นต้นประโยค
 
Example

- If  he studies hard , he will succeed , หรือ 
- He will succeed  if he studies hard.
- If she telephones, tell me at once.  หรือ
- Should she telephone, tell me at once.

Condition

2.  Present unreal

เหตุการณ์ที่เป็นไปไม่ได้ในปัจจุบัน

Structure

If +V (subj. + past)
, would + infinitive
(v.to be ใช้ were ทุกพจน์ )
หรือ ตัด if ใช้ were

Example

- If I were rich, I would buy a new car.
 (but I’m not rich) หรือ
- Where I rich, I would buy a new car. หรือ
- I would buy a new car if I were rich.

Condition

3.  Past unreal
เหตุการณ์ที่เป็นไปไม่ได้ในอดีต

Structure

If + V (past perfect)
คือ had + V3, subj + would
Have + V3 หรือตัด  If ออกใช้
Had + subj + V3 หรือ Subj.
Would have + V3 + If + had + V3

Example

- If she had been there, she would have
 seen the accident (but she was not there)
- Had she been there, she would have
 Seen the accident.  หรือ
- She would have seen the accident if
 she had been there.

 
Present subjunctive

request  advise   order   insist
purpose demand  prefer   ask
require  move   urge   suggest
commend recommend

subj. + v + that + subj. + (should) + infinitive without to
Ex.   She insisted that I (should) be here at seven o’clock
  I suggested that she (should) come early.
  The doctor advised that the patient be rest.

Present subjunctive

- It is necessary, important
- It is essential, imperative that
- It is advisable, better
- It is (my, his, etc.) wish that

Ex.   It is necessary that they (should) work harder.
 It is better that we (should) take the examination
 It is my wish that he (should) take her out to dinner.
 It is her wish that you (should) do that work.

Present subjunctive Past perfect subjunctive

wishif   as if
only
It’s about time
It’s high time
It’time
as though
supposed  supposing
would rather
would soon

-  past subjunctive กริยาคำหลังเหล่านี้ใช้ past tense (ไม่เป็นจริงในปัจจุบัน)
Ex.   I wish I were a millionaire. (but I’m not)
 If only he come.  (but he doesn’t
 It’s about time the class began.  (but it doesn’t)

-  past perfect subjunctive กริยาหลังคำเหล่านี้ใช้ past perfect (ไม่เป็นจริงในอดีต)
Ex.   It is time the students had had breakfast.  (but they didn’t)
 Supposing we had finished our homework (but we didn’t)