As far as I know there are no persuasive theories in metaphysics. By “persuasive” I mean one around which a consensus forms. There used to be some – for example in times past the majority of philosophers would assent to the principle of the first cause or the omnipotence of God. But all those theories are now seen as specious and metaphysical systems are as variegated as fingerprints.
The only form of explanation that humans have ever developed is to start with some agreed upon terms and principles, and then work up to new terms and principles by applying basic logic, essentially unchanged since Aristotle. This is the system crystallized in first order logic: some undefined terms, some axioms, and rules of inference; thence theorems.
The trouble with metaphysics is that everything, absolutely everything, is up for grabs, even the basic terms and axioms. Unlike the situation in number theory and geometry, there is no agreement among humans about what the fundamental objects of the theory are, much less what properties they have. Evidently evolution has provided us with strong and reliable intuitions about space and time, but not about the nature of being. After thousands of years of thought metaphysics is still stuck at square one: what are the basic objects under discussion?
The Christian scholastics tried to make God the basic undefined term, and proceeded to paint themselves into corners. Since God was to be unexplained, God had to be “simple”. This use of “simple” is not encountered much any more; evidently to a scholastic God was simpler than peanut butter, since my jar of Jif contains peanuts, sugar, and vegetable oils, which can be further broken down into hydrogen, carbon, oxygen, etc., but God is just God all the way through. Thus we got the self-caused cause and negative theology.
Eventually philosophers realized that if they were willing to suspend the Principle of Sufficient Reason for God, why not suspend it earlier in the grand causal chain of Being? Why not an uncaused universe rather than an uncaused First Cause? After all, despite the effort of the scholastics to reify otherwise, everyone realizes that an omnipotent, omniscient, eternal deity isn’t really any “simpler” than the universe as a whole.
The problem of consciousness is similar. Our mental worlds are ungrounded. Before any mental concept we can always ask Why or What or How?, recursively. The metaphysics of consciousness seems equally at square one. The current hot idea is to ground the system in the undefined terms of qualia, which evidently are “simple” conscious experiences. No thought is ever given to how qualia themselves can be explained. Another problem with this is that we would need at least a small library of qualia to ground human consciousness. Perhaps this notion should be combined with Chomsky’s idea that evolution has engineered human conceptual space into more or less fixed lexical units. That wouldn’t satisfy the qualiists, but it does me.
It suggests that human consciousness is in one sense logically grounded in axioms implicit in the brain, and in another sense ungrounded – when viewed from the inside. From the inside our consciousness is circular. We are never at loss to explain an idea, but we frequently have to use more complicated concepts to do so. (Johnson used “reticular” to define “net”.) That doesn’t really bother most people, just lexicographers and philosophers.
For me consciousness is best viewed as a a relational system, which is “grounded” in emotions. When your brain gets tired of explaining itself it just broadcasts pleasure or pain, or some other emotional qualia. Emotion has the virtue of stopping thought and motivating action.
This deflationary view of consciousness is the one I’m drawn to intellectually, but emotionally I still like the idea of immortal souls. So I don’t begrudge the qualiists their fun; I actually hope they’re right.
Colin McGinn is certainly right to think that the “hard” problem of conscious cannot be solved, and just about anyone who has thought seriously about it for five minutes will agree. In my terms, there is no way the brain can give an inner explanation for the Chomskian elemental concepts that the mind cannot account for reductively but feels it understands heuristically. In more general metaphysical or logical terms, there is no way to explain qualia in that doesn’t invite further questions that demand further explanations.