A pronoun does not stand for a noun as the name suggests.
        subordin
subject slot, an object slot, adverbial slots, etc.
 
They can be used on their own as in 'Why?' - 'Because there was no
time.' This is a function in a 'communicateme' - a structure on one of
the text levels.
 
Subclauses can fill functional slots in mini-paragraphs, e.g.
conditional structures:
    If this is so,     topic slot
    then xxx           conclusion slot.
Etc.
 
Once we have described the syntactic rules concerning subclauses, we can
then look at their position in sentences, communicatemes, paragraphs and
so o
subclause comes first, it usually refers to some information we already
know. If it comes last, focus is on the information it contains - which
has to do with our memory span, something biological, rather than linguistic.
 
Why we may want to put this information in focus, may have innumerable
reasons - this has to do with life in general. Maybe the information is new
to the hearer, or we find it fascinating, or we want to set right what
someone else has said, and so on.
 
My 2 cents worth ...
 
  Burkhard Leuschner
  Paedagogische Hochschule,  Schwaebisch Gmuend,  Germany
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