[quote=@Guilty Spark]
[@Letter Bee] That's a pretty sweet idea. And I understand the dilemma I was having; I thought that we were constructing these summoned creatures with our imagination, but we're [i]actually[/i] calling upon extradimensional entities. 
[/quote]

It's actually a mix of that. You construct the creatures' [i]forms[/i] with your imagination, but the creatures' [i]conciousnesses[/i] come from somewhere else.