Anyway, into the rabbit hole. I'll be replying in a more conventional style, hitting what I feel are the more relevant points:
If one claims that metaphysics is simply vacuous speculation that can obtain no knowledge, and that it cannot answer any questions that science cannot, then this is itself a metaphysical assertion!A key part of my argument is that I think the term 'metaphysics' is ambiguously defined, as is the notion of what constitutes a 'metaphysical question'. I think the historically shifting, broad, and often non-specific use of the terms makes my argument for me, and that's a case of what we're running into here. I don't see any reason to entertain the idea that such an opinion of metaphysics is itself metaphysical – it's just a statement about metaphysics. Of course, one can define metaphysics in a myriad of general and ambiguous ways, as well as find some philosopher or another who has employed a given definition. But there's a clear lack of consensus on what metaphysics is, how it's supposed to be applied, what types of problems it can help us solve, and how it helps us do it.
Next, Steven replies to my thoughts on Model-Dependent Realism, or MDR:
For a claim about one’s epistemological relationship to reality is still metaphysical. In fact, epistemology is widely seen to be subsumed under the umbrella of metaphysics. Why? Because a claim about our relationship to attaining knowledge about reality is still a claim about the nature of reality, since we are a part of reality.Model-dependent realism does not make claims about what constitutes reality; the entire point is that it jettisons the question of what is 'real' entirely. Steven's position seems to be predicated on the idea that Absolute Truth is 'out there', and that we can somehow know this reality independently of models.
But under MDR, whether absolute truth is out there is not an issue. MDR simply favors reliable models over unreliable ones. And, as Hawking notes, each model can itself be seen as its own reality. Now, we have good reason to believe that there's an absolute reality beyond the scope of our models, but that is because a wide array of reliable models overlap and confirm the same phenomena. So the belief in an absolute external reality is an assumption based upon observation. Whether one considers this a 'metaphysical' position is, given the ambiguity of the term, not really relevant.
Steven then gets to the meat of our disagreement with the use of semantics:
I never said that we can know what exists beyond our experience. Rather, I said that we can know that certain metaphysical principles will apply beyond our experience—if there is such a thing. Therefore, I never claimed that we can have cognitive access to anything that is not observably accessable to us.I'm confused here. If we can't know whether there actually is anything 'beyond our experience', then it's nonsensical to suggest that metaphysical principles would still apply to it, precisely because these metaphysical principles are abstracted from and given meaning by our experience.
I claimed that necessary concepts like identity, and essence and propositions like the laws of logic can, and must be, predicated of any existing thing—not words like beyondThe word 'beyond' is a spatiotemporal metaphor that Steven used to describe the ability of the laws of logic to describe supernatural/non-empirical/non-spatiotemoral phenomena; my point is that the very act of doing so, of cantilevering a semantic structure derived from empirical experience into realms purportedly beyond it, renders the semantic structure meaningless.
This is illustrated by the fact that one cannot know if something exists at all unless it is part of our empirical experience. We can certainly conceptualize all kinds of things, but in doing so we conjure representative abstractions, not extant objects. Take for example the old ontological argument, which posits that God exists because he exists necessarily – that is, God is the 'greatest conceivable being', and a being that has the property of existence is conceivably greater than one that doesn't. But something must exist in order to have any properties at all; conceptual entities (like, say, unicorns) have conceptual abstractions of properties.
The problem in the ontological argument is semantic: the semantic framework derived from empirical experience is being used to make assumptions about things that are purportedly 'beyond' empirical experience. But a closer examination of the linguistics used reveals that the argument is chock full of question-begging and equivocation.
Steven then goes on to give a mathematical example, saying that it's both consistent with the laws of logic. He anticipates my objections, mostly correctly:
I know Mike will respond that the set (III) is not an actual existing “thing”, in that we cant go out and find the set (III) in the empirical world, and that it is only a representation of empirical things. There are two answers here: 1) even to claim such a thing defeats Mike’s overall position—the death of metaphysics—since such a claim is metaphysical, and 2) a representation or concept can and does still have properties.Pointing out that a set is a cognitive abstraction is simply an observation, not a metaphysical claim – though again the ambiguity of metaphysics rears its head. And, as I pointed out above, a representation or concept does not have properties – it has conceptual abstractions of properties – i.e., 'if X existed, it would have Y properties'. And whether or not a conceptual abstraction actually corresponds with reality requires the construction of testable models of reality.
That is why, to paraphrase Sean Carroll, if you want to know what reality is, you can't just think about it – you have to go out and look at it.
Update: Steven has replied here.