I know about the logical expression of 'if --- then', such as 'If the temperature reaches or exceeds a particular temperature, then the kettle will turn off.'

But what about situations that involve 'when'. For example - 'When we see the signal, then everyone can begin to raise their hands'.

I was 'googling' for information about this, but have found nothing so far about this. But I'm definitely interested to find out whether it is feasible to use 'when' followed by 'then'. Thanks all!

2 Answers 2


From a standpoint of Logic, the difference between if A then B and when A then B is that in the if-then formulation the event A is possible, but not inevitable -- A can be true but is not guaranteed to ever be true.

For the when-then formulation, it's slightly different because A is possible AND inevitable, or stated another way the event (or condition) A will be true at some point in time. If it's possible that A never becomes true, then when-then devolves to if-then

  • Thanks so much to you both for your help! The explanation about when-then is excellent! That definitely makes sense. Thanks again. Greatly appreciated!
    – Kenny
    Jun 21, 2021 at 3:44

It's perfectly grammatical to start a sentence with "then" and therefore you can open the main clause with it.

I noted it emphasizes the temporal element,as if to say "and not before."

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