User blog comment:General MGD 109/Soul problems/@comment-3045936-20120215213615

That is something unknown. But maybe there is a different between Souls, Ghost/Spirit, and Demons. Like maybe only human souls and monsters with souls as they were once human. As maybe something in Hell alters the soul enough. But according to Castiel a soul is pure energy and energy cannot be destroy or created just rechanneled at least scientifically.