I am a little confused about using "when v-ing" and "while v-ing". When should I use "when v-ing" instead of "while v-ing" ?

1- Always keep some change with you. It’s useful when buying a bus ticket.

2- Always keep some change with you. It’s useful while buying a bus ticket. (The dictionary say this usage is wrong)

3- Be careful when crossing the road.

4- Be careful while crossing the road. (Is it correct to use while here? )

5- I used to read a book when using public transport.

6- I used to read a book while using public transport. (Again, is it correct to use while here?)


"We can use while to talk about two longer events or activities happening at the same time" (Cambridge Dictionary).

You can use "while" only in the examples 6, and maybe 4, because only there you have two longer events happening at the same time. (I personally do not feel that crossing the road is a "long event," though). So, both events need to be longer, which means, they are happening in a period of time rather than in a moment of time. But you could also use "when," as in the example 5.

You can always use "when," but you can use "while" only for two longer events.

So, 1, 3, 4, 5 and 6 are correct, but 2 is not.

There's a very clear presentation of using when and while on Grammar-Quizzes.com.

  • Thanks. I know that rule but I thought there might be something else to differentiate them. + I don't understand why "crossing" is not a long event. – Talha Özden May 18 '19 at 9:26
  • But I see some sentences like: "Be careful while driving." . I don't think if we want to use "while", there must be two longer events. – Talha Özden May 18 '19 at 9:31
  • I updated my answer. Driving is a long event, so being careful while driving is also a long event - they both happen in a period of time. You could say that crossing the road is also a long event and say "be careful while crossing the road," but to me it does not sound well, because you cross the road "at once," - so it's not really a long event. – Jan May 18 '19 at 9:59
  • -1 The use of while has absolutely nothing to do with the length of an event, not even the length of an event in relation to another. I can knock a vase to the floor while sneezing—both of which take only seconds, and both of which start and end at the same time. – Jason Bassford May 18 '19 at 17:02
  • I mentioned the length as a "period" as opposed to a "moment," not the actual length. Different explanations of using when vs while exist - I found the two from the linked sites most convincing. Would you like to make your answer and explain it? – Jan May 18 '19 at 17:05

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