What are conditional sentences?
Sentences containing conditional clauses like if, unless and provided are called conditional sentences. They are four types and express four types of meaning.
Rules of Conditional Sentences
(a) Type Zero: It always expresses real and possible situations.
• If + simple present: simple present (for scientific facts
If you put
butter in the Sun, it melts.
If water is
boiled, it changes into water vapour.
• If + simple present: imperative
If you want to
win, play fair.
Study hard, if
you want to pass the exam.
(b) Type One: It expresses possible situations in the present or future.
• If + simple present: will/shall/can/may/must+ V1
I shall play baseball
if I get the chance.
If you come here,
I shall give you a chocolate.
If it rains, he
won't come.
(c) Type Two: It expresses doubtful situation/hypothetical condition in the present or future.
• If + simple past: would/should/could/might + V1
If they worked
hard, they would pass the exam.
If I were you,
I would never accept the proposal.
If she were a
bird, she would fly.
Note: 'Be' verb in if clause always becomes
'were'(only_in_conditional sentence type two)
(d) Type Three: It expresses regret / unfulfilled the situation in the past.
• + past perfect: would/should/could/might + have + V3
They would have
missed the bus if they had not left home in time.
If you had
given me a book, I would have completed the task.
He would have
helped you if you had asked him.
(e) Unless: if not 'Unless' has a similar structure like 'if' but it gives negative/situational meaning.
Unless you
study hard, you won't pass (will fail) the exam.
Unless you
complete your master's degree, you can't be a good teacher.
She wouldn't
learn much unless she worked harder.
(f) Provided that: if 'Provided that' functions like 'if'
Provided that
you were a teacher, what would you do?
Provided that
I were you, I would behave well.