What is the difference between the following sentences.

He was wrestling when he hurt his ankle.

He was wrestling when hurt his ankle.

Is it okay not to repeat the same subject, he in this case, after the word when or is it necessary?

Which one is more idiomatic?


The word when can take finite clauses as a Complement (clauses with a tensed verb). When we have a finite clause, the Subject of that clause must be present:

  • *He did this because was angry. (ungrammatical)
  • He did this because he was unhappy.
  • *She laughed, although was sad. (ungrammatical)
  • She laughed although she was sad.

This is not true about non-finite clauses, which do not have any tense:

  • Bob was sacked from his job, due to always being late.

In the sentence above the non-finite verb being does not need a Subject. It has no tense, it is a participle, not a tensed verb. We understand the Subject of being to be the same as the Subject of the verb in the main clause, Bob.

The Original Poster's example

The conjunctive preposition when can take clauses with tensed verbs. When these clauses have tensed verbs (past or present tense), they must have their own Subject.

Although the Subject of hurt is the same as the Subject of was wrestling, we need to use a full Subject for the second clause:

He was wrestling when he hurt his ankle.

He was wrestling when hurt his ankle. (ungrammatical)

  • @chepner Not really. Gerund-participles are not deverbal noun, they are verbs. Unlike deverbal nouns they can take Objects and other complements and are modified by adverbs and not adjectives. You can read about the difference here deverbal ing-nouns versus gerund-participles. Consider due to continuously taking bribes for example. – Araucaria - Not here any more. Apr 3 '16 at 19:51

If you leave out the second pronoun, you could write it like this:

He was wrestling and hurt his ankle.

dictionary.com includes this definition of "when":

upon or after which; and then:
We had just fallen asleep when the bell rang.

It needs a main clause after it because it is, in a way, joining two sentences. "This happened" when "this happened". Without the pronoun, "hurt his ankle" is just a fragment of a sentence.

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