I would really appreciate if someone could explain this to me.

He invented a weapon that was so dangerous that no one dared to use (it).

I was certain that there is no need for it here but a friend of mine disagrees. This is how I understood.

The first sentence (He invented a weapon) and the second one (the rest) are combined with the common element, a weapon. Thus, the initial a weapon stays and the second one gets replaced by that. On a closer look, I think that works as a subject relative pronoun (It was so dangerous) and also works as a object relative pronoun (No one dared to use it).

My questions are:

From the original sentence, which is grammatically correct, with or without it?

In my opinion, in order to insert it, the sentence should be: He invented a weapon and it was so dangerous that no one dared to use it. Is this correct?

Is it correct to use one pronoun as the both usage of subject and object inside the same adjective clause?

Thank you!

  • The only way to omit "it" would be to recast the sentence as He invented a weapon that was (too) dangerous to use.
    – BillJ
    Jan 21, 2022 at 12:55

2 Answers 2


The word "it" is necessary in that sentence. In the construction "so X that Y", the "that" does not act as a relative pronoun at all. Y is always a clause on its own: in this case "no one dared to use it". The word "that" is not a part of the clause.

For that reason, sentences such as "the bread was so tasty that I had for breakfast" are ungrammatical.

EDIT: I misunderstood the original question. So to answer it: can the first occurrence of the word "that" in the original sentence act as both a subject relative pronoun and an object relative pronoun?

Theoretically, it could:

He invented a weapon that was so dangerous that Y and [that] no one dared to use.

In the above, the second "that", which is in square brackets, is not necessary; so the first "that" can indeed play both roles simultaneously.

The problem with the original sentence is that it's not possible to parse "that no one dared to use" as part of the outer clause. Because "no one dared to use it" immediately follows "so X that", it can only be interpreted as the argument Y in "so X that Y". In that context, the clause has no relative pronoun introducing it and so has to explicitly include both subject and object.

  • Hi, thanks for the comment. Actually the that I’m referring to is that as in … a weapon that was so … (I’m aware of the fact that that in the expression so … that … is not relative pronoun.) My question was if this that can work as a subject relative pronoun and object relative pronoun at the same time in the following clause. I’d like to know if that in this case can work as a subject relative pronoun in ‘was so dangerous’ and an object relative pronoun in ‘no one dared to use’ at the same time inside this clause.
    – lolxi
    Jan 21, 2022 at 0:20
  • oh! very interesting, I'll update my original answer
    – PoolOfPeas
    Jan 21, 2022 at 0:27
  • So the problem is that it is difficult to parse the last part with that! I understand now, thanks for the update!
    – lolxi
    Jan 21, 2022 at 0:57
  • Importantly, the expression that no one dared to use it is an 'indirect complement' licensed by the "so" that modifies "dangerous".
    – BillJ
    Jan 21, 2022 at 11:45

He invented a weapon that was so dangerous [that no one dared to use (it)].

The verb "use" is transitive here, so in this case the object "it" is required.

The whole of the expression "that was so dangerous that no one dared to use it" is a relative clause with "weapon" as antecedent. The relative word functions as subject within the relative clause. But "that" is not an object relative pronoun; rather, it is a pro-form acting as object of "use" that refers to "weapon".

Note that the bracketed expression is called an 'indirect complement'. It is called this because although it is complement of the adjective "dangerous", it is licensed by the adverb "so" that modifies "dangerous". We know this because if we drop "so" the adjective phrase becomes ungrammatical.

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