If they hadn't spent years in their laboratories, they wouldn't have had the expertise they needed.
Every conditional has an if-clause (the condition) and a result clause. The tenses you choose show whether the situation is real or imaginary.
If you carry out this experiment, you will see interesting results.
The world would be a different place if we didn't have them.
if + no will
if + no would
Zero and first: present after if. Second and third: past or past perfect after if.
Zero: if + present, ... present · First: if + present, ... will + base verb
Zero only: you can swap if for when and nothing changes.
Second: if + past simple, ... would + base · Third: if + past perfect, ... would have + p.p.
After if, use were for every person: If he were here...
If you heat ice, it melts.
a general truth
If you carry out this experiment, you will see results.
a future possibility
If I were a scientist, I would work in a lab.
a hypothetical present
If I had been there, I would not have noticed it.
a hypothetical past
If it will rain tomorrow, we will cancel.
Correct: If it rains tomorrow, we will cancel.
If I would have known, I would have told you.
Correct: If I had known, I would have told you.
If she studies medicine, she will works in a hospital.
Correct: she will work in a hospital.
He wouldn't ^ discovered penicillin.
Correct: he wouldn't have discovered penicillin.
Say the answer out loud — then tap to check.
If she had knownA about the meeting, she would comeB, butC nobody toldD her in time.
Bshe would come → she would have come
✓ third conditional: would have + past participle
If my colleagues was hereA, they would confirmB the figures, butC they areD both on leave.
AIf my colleagues was here → If my colleagues were here
✓ my colleagues is plural → were
If you heatA ice, it meltsB; andC if you will heatD it further, it eventually boils.
Dif you will heat → if you heat
✓ no will in the if-clause
Name the conditional you use in each answer.
Never put "will" or "would" in the if-clause.