Predicate nominative in Koine

I am looking for some current thinking on the use of predicate nominative 
in Koine, although such thinking may take into account historical 
perspectives on the subject. Is there a *best rule* ? Can we have any 
certainty regarding word placement in specific instances where the 
predicate nominative is used? I am particularly interested in Johannine 
use, but are there any characteristic differences between the various NT 
writers on this point - either from your own work or other sources you 
can cite?


Chuck Arnold