I saw this structure in a few texts, and it made me wonder what is the grammar role of when in this sentence and why the subject and verb (he is) are absent. It doesn't fit any grammar structure that I know in English. I guess the part after when is an adjective clause but I'm in doubt since the clause lacks the subject and verb.

2 Answers 2


Because it is common in English to omit certain words from certain subordinate clauses when they can easily be inferred. This is called ellipsis.

It can sometimes lead to ambiguity, but here the omitted subject can only refer to the subject of the main clause, “he,” as there is no noun or other pronoun to refer to. If a different subject were intended, ellipsis would not be permissible.

He gets angry when I am trying to explain this.


He is can be omitted because it isn't necessary. Reading the sentence, you know who is trying to explain the issue: he is!

When... functions as an adverb clause, because it modifies the verb phrase gets angry -- it is saying when he gets angry.

When: https://www.ahdictionary.com/word/search.html?q=when

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