But this sort of reminds me of my long-standing attempt to figure out what Friston-style models are doing that PCT-style models aren’t (and vice versa), where actually the thing at play seems to be a question of “which underlying theory deserves more status?” than “what different predictions do these models make?”, in a way that’s quite difficult to resolve.
As far as differing predictions go, if IFS’ model of how parts need to be treated is correct, then it should not be possible to directly alter someone’s rules without any reference to parts. Yet, the fact that non-parts-oriented therapies also work is a trivial refutation of this prediction. Ergo, the idea of parts is an unnecessary addition from a theoretical point of view.
As far as differing predictions go, if IFS’ model of how parts need to be treated is correct, then it should not be possible to directly alter someone’s rules without any reference to parts. Yet, the fact that non-parts-oriented therapies also work is a trivial refutation of this prediction. Ergo, the idea of parts is an unnecessary addition from a theoretical point of view.