I would like to know if i can use them interchangeably, because for example i see that are used as the verb "to include".
Is there some subtle differences besides that the first is a irregular and the second is a strong verb?
If you use it in the context of "including something", for example to your opinion, einbeziehen doesn't have such a strong meaning as einschließen. When you use einbeziehen you "take into account" or "also consider" something and when you use einschließen you "include" or "add" something to your opinion.
This is probably due to the fact that "schließen" means "locking" whereas "beziehen" means "relate" which doesn't give it such a conclusive character.
'Einschließen' suggests completeness, I.e. taking sth into account with regard to all of its relevant aspects and unconditionally. 'Einbeziehen' is weaker in the sense that though it is considered, it either is only partially or that its consideration may be overridden by some other influence that is taken into account.
