In my understanding, 'as we know it' usually follows a noun phrase and means like

  • The building as we know it = the version/condition of the building we know now.

First, I'm not sure about its grammar.

  • Is the 'as' a conjunction?
  • Is it correct to think that 'it' changes to 'them'? E.g., the buildings as we know them

Second, a question about its use.

  • Is it possible to use when the preceding noun is a pronoun? If yes, what should the 'it' be changed to?

I feel Tom as I knew him ten years ago will be understood. I'm not sure about He as I knew him, and even less sure about the case of second person pronoun. For example, if I want to say 'You have change a lot', is it possible to say like You are so different from you as I knew you?

I guess a more usual way to express the last sentence above would be You are so different from the person I knew you were. If this works, what happens if I'm talking to plural you? Making person plural (...from the people I knew you were) looks a bit strange to me.

  • 2
    Yes, as we know it can be inflected to suit the situation (as I knew him and so on), but I think the most natural way to express your sentence would be You are so different from the person/Tom I used to know. Jul 17, 2022 at 7:46
  • @KateBunting I see, even then, would you say You guys are different from the people I used to know?
    – sundowner
    Jul 17, 2022 at 9:56
  • 3
    Yes, you can. It's a common construction, but it's not a fixed phrase, so its parts can be inflected normally. OTOH, if some particular way of doing that sounds weird to you, don't say it -- trust your internal grammar; it actually knows all the rules, even if you can't state them consciously. The way it raises a flag is to make it feel weird, so pay attention. Jul 17, 2022 at 14:02

1 Answer 1


As in this context serves to introduce a comparative clause.

[the building [as [we know it]]]

The comparative clause has a meaning close to:

We know it to be this way.

This is not a set phrase, so all the words can inflect or be swapped out depending on the context.

the buildings as we know them

the building as we knew it

the building as I knew it

the building as he imagined it


This means that the phrase 'as we know it' is not in fact an idiom - it can be readily understood from its component words and their normal grammatical relations in English.

Though as can be found assigned to the nebulous 'conjunction' category in many dictionaries and older grammars, it's best categorized as a preposition and is thusly categorized by respected modern grammars such as the Oxford Modern English Grammar and the Cambridge Grammar of the English Language.

As far as using that phrase or any phrase headed by a preposition following a pronoun, it would have to be read as a supplement, and would usually be set off by a comma:

He, as I knew him then, would never have accepted a bribe.

An attested example:

New "successions" will take place; the changing Many will pass endlessly on in its phantom army, for ever appearing, and forever falling back into the One: but he, as we knew him, will awake no more, ah, nevermore! (SUGGESTIONS LITERARY ESSAYS; Ernest Edward Kellett; 1929)

This is a rather rare usage though, and perhaps better avoided in everyday writing.

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