Within some religious traditions, the purpose of Creation is for God to express Himself.
'God speaks everywhere, through creation as through his word. This is the meaning of creation. As St Paul said, "The invisible things of God are made known by the things that are made." Or in the hadith attributed to Mohammed: "I was a hidden treasure and yearned to be known, so I created creatures, in order to be known in them." ' [Christopher Bamford, Parabola, Fall 2006]
Atheists sometimes use a form of POSIWID to try and explain away religion, especially primitive forms of religion. Imagine a tribe struggling against the elements (weather, animals, crops, and so on). If these elements have some strong effects, then it seems to make sense to think of some purpose behind these effects. And this seems to imply the existence of some purposeful entity - one or many gods.
Having constructed this imaginary argument for the existence of one or many gods, atheists can then try to attack it in two places. Either they deny that every phenomenon has to have some purpose. (Perhaps there just isn't a "system" in that sense.) Or they deny that every purpose has to have an owner. (If there is a system, it is an "emergent" system.)
But by the Middle Ages, religious thinkers were using POSIWID in an entirely different way, as illustrated by the quotations above. They start with the notion of a purposeful entity (God) and then try to infer His purpose from his actions. Why on earth would God create stuff, miserable creatures like us, what reason could He possibly have?
As a thinking tool, POSIWID is essentially agnostic - it works with the assumptions you provide. If you think you can identify some purposeful entity (whether natural or supernatural), then it can suggest what the purposes of this entity might be. Alternatively, it may suggest the existence of previously unsuspected entities. Use with caution.
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