There are two sentences like below,

  1. I want to see the house in which you lived. (O)-correct
  2. I want to see the house in that you lived. (X)-incorrect

We learned that we should not put a preposition in front of that (relative pronoun). But we don't know the reason why we should not put a preposition in front of that. I want to know the reason.

  • 1
    "I want to talk about that" and "I want to go up that mountain" are both grammatically correct. I think your confusion is more about the difference between 'which' and 'that.'
    – Elijah
    Jul 7, 2015 at 7:45

2 Answers 2


The answer (which I had some difficulty accepting, but now agree with*), is that that is not a relative pronoun at all, but a complementiser. It is the same that as in

He said that he was going

So, on this analysis

The house that you bought


The house which you bought

have different structures, and both relate to a (now obsolete) form

*The house which that you bought

This is found in Early Modern English, but in Modern English at least one of which and that must be omitted.

Since that is not a pronoun (a noun phrase) but something different, it cannot follow a preposition; so in the theoretical underlying

*The house in which that you lived

the that must be omitted, but the which cannot be.

*There was a long thread on this forum a couple of years ago where somebody said this, and I disputed it, but they eventually convinced me. I haven't been able to remember what to search for it by, though.

  • +1, for the interesting info about the relative word "that" functioning as a clause subordinator. :)
    – F.E.
    Jul 7, 2015 at 8:33
  • Very nice. Can you possibly expound on how exactly you tell this "that" (complementiser) from the other "that" pronoun which that seems to be used in "I am gonna climb up that wall of rock in Yosemite." Is it just by checking if you could replace it with "which"?
    – DRF
    Jul 7, 2015 at 8:59
  • 1
    @DRF, that can be a pronoun, but in your example I would call it a determiner. As you suggest, the way to determine the syntactic role of a word or phrase is to see what might substitute it (though it's not always a straight yes/no answer). That that could be substituted by the, my, or which; and you could not use more than one of those four there. As far as I know, that as a complementiser (or subordinator) is one of a kind, and can't be substituted in Standard English (though in some dialects where and how can function in the same way with certain matrix verbs ... continued
    – Colin Fine
    Jul 7, 2015 at 9:35
  • 1
    ..continued) This last can be confusing, because in I saw how you did that, how is not a complementiser, but has a semantic function comparable to what in I saw what you did. The dialect usage I'm referring to is I heard how he went back again, in the sense I heard that he went back again, referring to the fact of his going back, not the manner of it.
    – Colin Fine
    Jul 7, 2015 at 9:38

I don't know whether the given explanations are convincing. They are complicated and far-fetched. As I am German, I compare English that with the German definite article der, die, das. These forms also have demonstrative power as in English. You can say

  • Das ist mein Haus. That is my house. In low/ northern German: Dat (hus) is min hus.

  • This is the house (that) we lived in.

In my view such a construction comes into being from three sentences:

  • 1 This is the house. -- 2 What house? -- 3 That house (which) we lived in.

Part 2 is meant as the question of a second person. Part 3 is the answer of the first person. As "that" in part 3 has still its article and demonstrative character a preposition is not placed before. In

  • the house that we lived in

"that" has kept some of its demonstrative chracter and the preposition in rather belongs to "which" in part 3.

I would never try to explain such historical things to a learner. He will probably understand nothing because he has no idea of historical language processes over more than thousand years and how several independent sentences can grow together into one sentence.

So I would answer the question why is it not possible to place a preposition before relative that with that's how it is. The historical reason for this would take too long to explain and will hardly help you.

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