I am no expert, but I think if you look through the historical documents (folklore, trial records e.t.c.) then you will find that in most cases those who were accused of being witches or made claims of magical ability were considered to have obtained that ability as a result of some kind of pact. This is usually either with "The Divell", some other demon, or with some spirit from Faerie (especially in Ireland).
So, from this point of view the person posting on their blog (which I didn't read) could be considered correct. The historical evidence suggests that witches derived their power from pacts with spirits. Whether you accept that or wish to take alternative arguments under consideration is up to you! (IMG:
style_emoticons/default/smile.gif)