Something I question daily is whether I should put a complement in a sentence or not when it comes to relative clauses. For example:
Bullying ought not to be something that you should just "brush [it] off".
I love [it] that you like knitting.
I like [it] when you are at home.
Should I include it in those sentences, or I could leave it out just fine and there'd be no problem? What is the general rule at play here?
[1] Bullying ought not to be something that you should just "brush [it] off".
[2] I love [it] that you like knitting.
[3] I like [it] when you are at home.
In [1] "it" cannot be inserted. In the relative clause, "brush" already has an object understood as "something", so inserting another object would be ungrammatical.
In [2] "it" is obligatory in Standard English. This is not a relative construction but an object extraposition construction, where the dummy pronoun "it" appears as object and the content clause "that you like knitting" as extraposed object.
In [3] "it" is also obligatory: it functions as object of "like". This construction bears some resemblance to extraposition, but it differs from extraposition in that the final clause, "when you are at home", is not a potential replacement for "it".
The first sentence is different from the second and third. In the first, the subordinate clause ("that you should just 'brush off'") already has a complement (direct object): the relative pronoun "that". Therefore, it would be incorrect to add another.
The second and third sentences use a "dummy pronoun" ("it") as the complement (DO). We can then use a nominal clause later in the sentence to represent the same thing as "it".[1] This is a common construction (it can be considered a kind of "extraposition") and is entirely correct. However, it would also be correct to omit the dummy pronoun and simply let the nominal clause be the complement (DO).
[1] I prefer to consider it a nominal clause. You called it a relative clause, and that's another possible approach.
