“Will” after “when” in English

We never use the future tense in time clauses (introduced by phrases like “after”, “as soon as”, “before”, etc.) in English. Should we need to express the idea of something happening, say, after something else in the future, we use the present tense in the time clause and the future tense or a command in the main clause. For example:

When we use “when” as a conjunction introducing a time clause, the same rule as for other time clauses applies:

In the cases in which “when” doesn’t introduce an adverbial time clause, we do use “will” when expressing the future. Most importantly, we use it when asking questions:

Things get a little complicated when the question is indirect. The “when” part then looks like an adverbial time clause, but it is not. For example, if the original question was, “When will you know the results?”, we can ask:

The second sentence is grammatical, but it is a different question! In the first case, you ask when (i.e. at what time) the other person will know the results, so the answer would be something like “at 5 o’clock”. In the other case, you ask the person to let you know after they get the results, so they would wait until they get them (e.g. until 5 o’clock) and then tell you, “I just got the results.”

Sometimes, it is harder to see that the structure is that of an indirect question. Consider the following examples:

The sentences could be rephrased as:

Both questions are grammatically correct, but only the first one asks about the specific time when “he will come”. The present tense in the other one indicates we ask about what happens habitually (such as every day or every week). The question is in the present because the answer would be in the present too, e.g. “He usually comes at 5 o’clock.”

Finally, “when” can be used to provide further information about a particular point in time. Compare the following two sentences:

They should be understood as follows: