Intro Subordination

Syntactic functions of subordinate clauses:
Subject: that we need a new computer has become obvious.
Od: he doesn’t know what to do.
Oi: you can tell whoever is waiting that I’ll be back in ten minutes.
Subject Complement/ subject predicative: one result is that the cost of the construction of the college will be very expensive.
Object Complement/ object Predicative: I know her to be reliable.
Adverbial: when you see them, give them my best wishes.
In addition, subordinate clauses may function within these elements:
Postmodifier in a NP: few of the immigrants retained the customs that they had brought with them.
Adjectival complementation: we are happy to see you.

Subject: that the invading troops have been withdrawn has not frightened us.
Od: I noticed that he spoke English with an Spanish accent.
Sc: my assumption is that interest rates will soon fall.
Appositive: you criticism, that no account has been taken of psychological factor, is fully justified.
Adjectival complementation: we are glad that you are able to join us on our wedding anniversary.
!!!!!!! But when the that-clause is a Od, complement or extraposed subject, the conjunction that is omitted except in formal use.
Ex: is a pity you don’t know Russian.  Extraposed subject
That cannot be omitted in a subject clause since without the subordinate marker the clause would be initially misinterpreted as a main clause:
Ex: you don’t know Russian is a pity*
    That you don’t know Russian is a pity.

Subordinate wh- interrogative clauses occur in the whole range of functions available to the nominal that clause and may function as a prepositional complement.
Subject: how the book will sell depends on the reviewers.
Od: I can’t imagine what they want with your address.
Csubj: the problem is who will water my plants when I am away.
Appositive: your original question, why we didn’t report it to the police...