As an Example, I want to refer to this Wikipedia article where there are many conditional sentences. Some of them drop the "then", some of them use it. When I change that (drop it where it was used or add it where it was dropped) then some still sound correct, but some sound a little odd, though all of them are still grammatically correct.
Originals:
- If you heat water to 100 degrees, it boils.
- If the sea is stormy, the waves are high.
- If it's raining here now, then it was raining on the West Coast this morning.
- If it's raining now, then your laundry is getting wet.
- If it's raining now, there will be mushrooms to be picked next week.
- If he locked the door, then Kitty is trapped inside.
Changed:
- If you heat water to 100 degrees, then it boils.
- If the sea is stormy, then the waves are high.
- If it's raining here now, it was raining on the West Coast this morning.
- If it's raining now, your laundry is getting wet.
- If it's raining now, then there will be mushrooms to be picked next week.
- If he locked the door, Kitty is trapped inside.
Questions:
- Is there a term for dropping "then" in conditional sentences?
- Are there any guidelines on when it can be dropped and when it must be retained?
EDIT:
There is an existing question ( Can I use an "if" clause without "then"? ) but that is more of an "YES/NO" type of question and it has been answered with "YES". Here, the question "When" in terms of guidelines : When it is useful to drop ; When it is useful to retain.