"as we know it" vs "as we know"

[Iwanna]

the life as we know it
the world as we know it

It is regarded as a relative clause. But because of the existence of 'it' , how could it be an adjective clause? What part of the clause is substituted by the relative pronoun('as' here)?

thanks

[Esl_Expert]

Hello Iwanna,

Your partial sentence refers to a particular type/manner/condition of world -- i.e. the one we know. The word "as" basically means something similar to "the way in which" or "the way that". So you might think of your partial sentence this way:

- the world the way/condition in which we know it

The following sentences all mean roughly the same thing:

- This is the world as we know it.
- This is the world the way we know it.
- This is the world that is the one we know.
- This is the world (that) we know.

By the way, the expression "life as we know it" generally is not used with the word "the".

- life as we know it

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"Education comes from within; you get it by struggle and effort and thought."

[Iwanna]

Thank you very much.