Which seems to suggest that epiphenominalism either begs the question,

Well, they do have arguments for their positions.

or multiplies entities unnecessarily by accepting unjustified intuitions.

It actually seems very intuitive to most people that subjective qualia are different from neurophysical responses. It is the key issue at stake with zombie and knowledge arguments and has made life extremely difficult for physicalists. I'm not sure in what way it's unjustified for me to have an intuition that qualia are different from physical structures, and rather than epiphenomenalism multiplying entities unnecessarily, it sure seems to me like physicalism is equivocating entities unnecessarily.

So my original argument disproving p-zombies would seem to be on just as solid footing as the original p-zombie argument itself, modulo our disagreements over wording.

Nothing you said indicates that p-zombies are inconceivable or even impossible. What you, or and EY seem to be saying is that our discussion of consciousness is a posteriori evidence that our consciousness is not epiphenomenal.

Unlike the other points which I raised above, this one is semantic. When we talk about "knowledge," we are talking about neurophysical responses, or we are talking about subjective qualia, or we are implicitly combining the two together. Epiphenomenalists, like physicalists, believe that sensory data causes the neurophysical responses in the brain which we identify with knowledge. They disagree with physicalists because they say that our subjective qualia are epiphenomenal shadows of those neurophysical responses, rather than being identical to them. There is no real world example that would prove or disprove this theory because it is a philosophical dispute. One of the main arguments for it is, well, the zombie argument.

3 doesn't follow from 2, it follows from a contradiction between 1+2.

Well, first of all, 3 isn't a statement, it's saying "consider a world where..." and then asking a question about whether philosophers would talk about consciousness. So I'm not sure what you mean by suggesting that it follows or that it is true.

1 and 2 are not contradictions. Conversely, 1 and 2 are basically saying the exact same thing.

1 states that consciousness has no effect upon matter, and yet it's clear from observation that the concept of subjectivity only follows if consciousness can affect matter,

This is essentially what epiphenomenalists deny, and I'm inclined to say that everyone else should deny it too. Regardless of what the truth of the matter is, surely the mere concept of subjectivity does not rely upon epiphenomenalism being false.

we only have knowledge of subjectivity because we observe it first-hand.

This is confusing the issue; like I said: under the epiphenomenalist viewpoint, the cause of our discussions of consciousness (physical) is different from the justification for our belief in consciousness (subjective). Epiphenomenalists do not deny that we have first-hand experience of subjectivity; they deny that those experiences are causally responsible for our statements about consciousness.

and epiphenomenalism can be discarded using Occam's razor.

There are many criteria by which theories are judged in philosophy, and parsimony is only one of them.

Except the zombie world wouldn't have feelings and consciousness, so your rebuttal doesn't apply.

Nothing in my rebuttal relies on the idea that zombies would have feelings and consciousness. My rebuttal points out that zombies would be motivated by the idea of feelings and consciousness, which is trivially true: humans are motivated by the idea of feelings and consciousness, and zombies behave in the same way that humans do, by definition.

That's an assertion, not an argument.

But it's quite obviously true, because we talk about rich inner lives as the grounding for almost all of our moral thought, and then act accordingly, and because empathy relies on being able to infer rich inner lives among other people. And as noted earlier, whatever behaviorally motivates humans also behaviorally motivates p-zombies.

Indeed. The condensed argument against p-zombies:

I would hope not. 3 is entirely conceivable if we grant 2, so 4 is unsupported, and nothing that EY said supports 4. 5 does not follow from 3 or 4, though it's bundled up in the definition of a p-zombie and follows from 1 and 2 anyway. In any case, 6 does not follow from 5.

What EY is saying is that it's highly implausible for all of our ideas and talk of consciousness to have come to be if subjective consciousness does not play a causal role in our thinking.

Except such discussions would have no motivational impact.

Of course they would - our considerations of other people's feelings and consciousness changes our behavior all the time. And if you knew every detail about the brain, you could give an atomic-level causal account as to why and how.

A "rich inner life" has no relation to any fact in a p-zombies' brain, and so in what way could this term influence their decision process?

The concept of a rich inner life influences decision processes.

This was longer than it needed to be, and in my opinion, somewhat mistaken.

The zombie argument is not an argument for epiphenomenalism, it's an argument against physicalism. It doesn't assume that interactionist dualism is false, regardless of the fact that Chalmers happens to be an epiphenomenalist.

Chalmers furthermore specifies that this true stuff of consciousness is epiphenomenal, without causal potency—but why say that?

Maybe because interactionism violates the laws of physics and is somewhat at odds with everything we (think we) know about cognition. There may be other arguments as well. It has mostly fallen out of favor. I don't know the specific reasons why Chalmers rejects it.

Once you see the collision between the general rule that consciousness has no effect, to the specific implication that consciousness has no effect on how you think about consciousness (in any way that affects your internal narrative that you could choose to say out loud), zombie-ism stops being intuitive. It starts requiring you to postulate strange things.

In the epiphenomenalist view, for whatever evolutionary reason, we developed to have discussions and beliefs in rich inner lives. Maybe those thoughts and discussions help us with being altruistic, or maybe they're a necessary part of our own activity. Maybe the illusion of interactionism is necessary for us to have complex cognition and decisionmaking.

Also in the epiphenomenalist view, psychophysical laws relate mental states to neurophysical aspects of our cognition. So for some reason there is a relation between acting/thinking of pain, and mental states which are painful. It's not arbitrary or coincidental because the mental reaction to pain (dislike/avoid) is a mirror of the physical reaction to pain (express dislike/do things to avoid it).

But Chalmers just wrote all that stuff down, in his very physical book, and so did the zombie-Chalmers.

Chalmers isn't denying that the zombie Chalmers would write that stuff down. He's denying that its beliefs would be justified. Maybe there's a version of me in a parallel universe that doesn't know anything about philosophy but is forced to type certain combinations of letters at gunpoint - that doesn't mean that I don't have reasons to believe the same things about philosophy in this universe.

This post isn't about my theories. It should not take an abnormal conceptual effort to reject the proposition that "there are many worlds, but no particular number of them". It is, on the face of it, illogical, like a round square. It doesn't express a coherent idea. Should we spend time thinking about the possibility that true things are also false, or that reality is an elephant, or that time is actually running backwards? Maybe it's a good cognitive workout to think about such things, and just maybe, on a very rare occasion, nonsense will turn out to be sense. But hopefully you can see my point - that this dispute is on a different level from a dispute over whether it's reasonable to believe that there are other worlds, ten dimensions, disembodied souls, and other such hypotheses. Those hypotheses may be strange, but they are unquestionably logically well-formed. They have a meaning.

The same can not be said for "no definite number of worlds". If something exists, it can be counted (or given a cardinality, if it is infinite). The defense of vagueness about branches rests on analogies like the ink blot, but it's a false analogy, because the ink blot is "created" by perception, by definition, or by a rule. This is why I engaged in my speculative psychoanalysis about the imperial ego of the abstract theorist, who creates a map of reality which remains unfolded before their mind's eye, and who never gets around to considering whether the correctness of the map is consistent with the fact of their own existence.

The existence of the world (the existence of "a" world, the existence of "this world") is not a matter of definition, it is an elemental fact, and you can't treat its existence as resulting from the mere mental projection of a boundary onto an underlying continuum. If your underlying-continuum theory of reality doesn't contain objectively distinct structures, one of which corresponds to observed reality, then that is a problem for your theory, it's not a revelation about reality.

you have never in all your posts and comments addressed the fact that all the issues with probability and personal identity in Many Worlds can apply to classical systems too

In fact I have, but perhaps not recently. This very same reasoning also invalidates various attempts to be vague about the number of selves, or to have fractionally existing selves; but that is another unpopular conclusion (unpopular on LW), and one which perhaps experiences even more resistance than the argument against vagueness about worlds.

"Copy" implies having more than 1 object : The Copy and the Original at the same point of time, but not space. Dan(t=n) and Dan(t=n+1) are not copies. Dan(Time=n, Location=a) and Dan(Time=n, Location=b) are copies.

If this is true, why doesn't this count as straight-forward induction? It certainly looks like induction and if it is, why is this a philosophical rather than scientific case? Also, if we think CI and MWI make the same predictions what does it mean to say "tended to be more correct"? Doesn't that require experimental evidence falsifying one of the interpretations at a later date?

It is not scientific induction, since you can't measure elegance quantitatively. However scientists have subjective intuition based on the successes and failures of past other physical theories. This is what I meant by "philosophical edge".

Doesn't quite work like this so far, maybe there will be some good discrete model but so far the Plank length is not a straightforward discrete unit, not like cell in game of life. More interesting still is why reals have been so useful (and not just reals, but also complex numbers, vectors, tensors, etc. which you can build out of reals but which are algebraic objects in their own right).