A course book for learners of English I have to use (New Total English, Intermediate, Student's Book, page 57) says:

'For First Conditionals, we use when rather than if to show that something is 100 percent certain to happen.'

And an example appearing in the exercises where this rule is applied reads:

'I will miss everyone when I leave my job.'

which should then mean

'I will definitely miss everyone / I am sure of missing everyone / I am sure to miss everyone if I leave my job.'

Whether or not I leave it? Or does the sentence necessarily imply that I will definitely leave my job at some point in the future?

What is '100 percent certain to happen': my missing everyone or my leaving the job or both?

If it is both, as I suspect, then isn't the clause a simple time clause, not an if clause, since there is nothing hypothetical about it?

  • 2
    When introduces a future fact. If introduces a possibility.
    – user66974
    Apr 25, 2017 at 6:54

2 Answers 2


Case 1: you have made up your mind that you are about to leave. Better still, even others are aware that you are about to leave. In other words, there is no uncertainty in your intention, and others' understanding that you will be leaving soon. In this case - when works.

Case 2: There is a possibility that you might leave. You are still uncertain in your mind whether you want to leave, or whether you will get the opportunity to leave. In this case - if works.

That's how the uncertainty factor mentioned by you plays out. With language you don't just communicate what's in the words, but you also offer interpretations for multiple other things that are not in the words. Both sentences are correct in that they express that you will miss them - but if you say if I leave, you are also telling the audience that you are not sure yet, and if you say when I leave you are indirectly making it clear to them that the decision has been taken.

  • Fine answer! Re-reading this rather difficult-to-understand question, it seems to me to be OP's argument that 'if' and 'when' have the same meaning, at least in his specific example, because it is 100% certain to OP both that "I will miss everyone" and "I will leave the job" (if not now, then later; nobody keeps a job forever, which is very true!) -- OP also means to contend that the fact "I will miss everyone if/when I leave the job" is already true, whether or not I leave the job, now or later -- therefore OP sees 100% certainty all over this sentence and sees no need to use "if!" Apr 25, 2017 at 14:43

I understood your question only after having composed the first part of this answer, so please be patient and bear with me as you read me through:

Your question seems rather confusingly worded about the idea of certainty, and you yourself appear confused also about where to apply the interpretation of "certain to happen."

FIRSTLY, the use of 'will' rather than 'would' or 'might' in the first part of the sentence is what makes it clear that at least "I will miss everyone" is certain to happen -- here it is will that implies certainty, whether 'if' or 'when' is used for the rest of the sentence.

SECONDLY, if and when modify the meaning only of what follows, and each modifies it differently, with "if" denoting possibility and "when" implying a high degree of probability (I see no need to be 100% certain!)

If and when cannot be used to mean the same thing. THE MEANINGS OF IF AND WHEN ARE GRAMMATICALLY DEFINED AND NOT OPEN TO INTERPRETATION. (I use block capitals only to emphasise that their meanings are grammatically fixed.) Uncertainty becomes implied the moment you use if.

Therefore you cannot get the same meaning by using IF and WHEN.

HOWEVER, after re-reading your complicated question, I think you believe that there is 100% certainty in both parts of this sentence (I am sure to miss everyone and also sure to leave this job, now or later) and therefore you feel there is no need to use IF -- if that is what you mean, then you can certainly go ahead and use "WHEN" instead of "if" to construct this sentence!

  • I have often seen the use of the phrase "if and when" in the same context, as in "you can be sure to miss everyone, if and when you decide to leave the job" -- this usage apparently reduces the certainty implied by a flat "when" and places the probability somewhere between "if" and "when" -- please note that "if or when" would not be used instead. Apr 25, 2017 at 14:48
  • I think you are reading too much into the question. No one can say with certainty that they will miss someone 30 years in the future, or even one year in the future. The sentence refers to leaving the job in the near future. I suggest you either end your answer before HOWEVER, or considerably shorten the part after HOWEVER . But this is editorial advice only. I gave the answer +1 because the English was correct.
    – ab2
    Apr 25, 2017 at 19:42
  • Thank you for the suggestion! I shall shorten the last section of the answer and edit out those examples. Apr 25, 2017 at 19:46

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