Maybe the difference here, though a subtle one, is between
an answer to the philosophical questions, and
the answer. I could provide you with
an answer to the question "what did you have for breakfast this morning?". I could even have that answer analysed philosophically - if I said "a bucket of pigswill', we could say that that was not a good answer, it doesn't accord with experience (not one eats pigswill), nor with intuition (I wouldn't want to eat pigswill); if I said "toast and coffee", that would be a better answer, purely on philosophical grounds. But neither are
the answer, I could not possibly know
the answer. Even if I had CCTV footage of you having your breakfast, I can only get more sure. But at some point in this increasing certainty, for the sake of linguistic convenience only, we say we've got
the answer. That point is the point at which others agree with our results (maybe they check their CCTV footage as well, they ask a snoopy neighbour who watches you every morning and he corroborates), and at which we can repeat our results (CCTV footage is corroborated by direct observation, which is corroborated by thermal imaging, which is corroborated by the fact that two slices of bread are missing etc...). There is no such continual testing and corroboration in philosophy, so it can only ever supply
an answer, never
the answer.
In a sense, the argument that only science can answer questions in the objective, public domain is actually trivially true and not ground breaking at all. I could have my own justification (
an answer) as to why I think you even exist, why I can trust my memory, why I think that because the laws of physics were some way yesterday they will be that way again tomorrow, but these are my private justifications. I might talk with you about them and we could have a very interesting conversation, but at no point in time could I say that my justifications had any better claim to objective truth than yours. They might be more internally consistent than yours, but who's to say that internal consistency is a measure of success?
This is the problem with philosophy answering these question, I've yet to hear anyone talk about how we know when we have an answer. I agree entirely with your list of issues that science cannot speak on (although I disagree about morality, but we'll come to that), but you've not said how you know when philosophy has an answer. Science knows when it has an answer. All the while the theory is being tested and cannot be dis-proven, it is the answer. The moment a test comes along to disprove it, it's no longer the answer. The clever thing about science is it's only ever temporary, it only ever has the answer for the time being. I just don't see the equivalent with philosophy. A few possibilities to get the ball rolling, but I'd be interested to her what you think a measure of success would be;
- The theory matches our intuition - as you've already said with morality, what we call our intuition does not seem to deliver consistent results. maybe reality isn't consistent, but if that's the case, then all we have again is an answer, not the answer. There's no reason to believe your answer will apply to me.
- The theory is internally consistent - This is promising, but if 2000 years of philosophy has shown us anything it's that lots of things can be sufficiently internally consistent to sound plausible. None of this gets at the axioms that are at the heart of the investigations.
- The ability of an argument to persuade - Take a look at the PhilPapers survey, or David Chalmers's lecture in which he presents the results. There's not been an inch of persuasive progress on any of the major questions of philosophy in 2000 years, Almost all are still split 50/50. In fact the only areas where arguments have been more persuasive than others are areas where I suspect you personally (from reading your posts) would disagree. Most philosophers think there isn't a God, and most philosophers think there is a real world external to our minds. If we accept persuasiveness as a measure of the answer, then we should at least all be atheist realists., but we're not.
Personally, I find a lot of use for the idea of philosophy as justification. Stories we can tell ourselves about why we believe what we do so as not to be "crippled with doubt" as Russell put it. But they are just stories, no one is better than any other. Charles Dickens is not a 'better' author than Emily Bronte, and Kant is not a 'better' philosopher than Hume, they're all just offering something, you either like it or you don't, there's no argument to be had as to why one it more 'right' than the other.
Modern ethics is a classic case in point. I'm an ethicist by training so I've read a considerable amount of answers to ethical problems from various angles. I can honestly say that I've not come across a single example of an ethical problem for which the answer we were all looking for cannot be shoe-horned into whatever ethical theory you care to try. Never, in my entire career have I come across a paper from an ardent supporter of any ethical school where they take on a moral dilemma and say "Wow, Kant (or whoever) gives us a really counter-intuitive answer here, I suppose we'd best follow it though", or "Nope, Kant's got nothing on this one, it didn't work". If the answer is counter-intuitive, you can guarantee that some subsequent paper will come along to show how the intuitive answer was right all along. This is why I became convinced by ethical naturalism (although I've always been a moral realist) every ethics paper I've read seems to be working backwards, it seems to be 'trying' to find the answer the author knows already is right in whatever ethical system they're applying.
Basically we seem to start off with a series of moral dilemmas where we know the parameters of the answers we're looking for ("kill the poor" isn't one of them, for example), but we don't know which exact course of action to take form all the ones that seem intuitively to be viable.
We put these dilemmas through various ethical theories of the greatest ethical philosophers of all time.
And we end up with a list of possible answers depending on which particular application of which particular ethics you've applied, that matches almost exactly the list of possible solutions our intuition delivered us at the beginning of the process.
Philosophy has done absolutely nothing to narrow down that list.
What it has done is given us reasons why we might believe in any one of the solutions, which is no small thing, I think it's really important, but it's not answering anything.
Once I accepted this phenomenon as a feature of reality (a simple belief statement, but based on empirical data, as above), then it becomes possible to at least apply science to determine which of the possible solutions might actually deliver the results we're looking for. Science can't tell us what we 'ought' to be looking for, but that doesn't seem to matter. In my experience we're all looking for roughly the same thing anyway. You mention the deontologist who does not believe in "maximising well-being", or the priest who wants only to "do God's will", but in neither case do we end up with anything we didn't know already. Deontology says nothing more than the golden rule, which it has been demonstrated even monkeys know. God's will suffers from (or perhaps benefits from) Plato's concern that God wills it because it is right. In religions, god only seems to will things that communities at the time think are right. Do you think it's a coincidence that God seems a lot less insistent on stoning adulterers and ostracising homosexuals these days?
The biggest problem with understanding ethical naturalism, and I think Harris makes this massive mistake too, is to think that what we want is in any way simple or consistent. 'What we want' is a large collection of vague and brazenly contradictory desires for particular sensations. Mapping those onto the world to work out what actions to take to achieve them is complicated. Our understanding of the world has a huge impact, our understanding of our own desires does too, as does the timescale we ask the question over. I think you've over simplified ethical naturalisms, and so has Harris. It's more like this.
We desire feelings X,Y and Z (an a hundred others, but lets call X,Y and Z the ones we've labelled 'moral objectives'), this is taken to be a brute fact and although we don't know exactly what X,Y and Z are, we can derive then by looking at the common threads of all moral behaviour, looking at brain function and applying evolutionary principles.
We learn that, in the environment we're in, doing A delivers feeling X, doing B delivers feeling Y and doing C delivers feeling Z. Again, we can test these hypotheses by the means above.
So far, so simple, but the trouble comes in three forms;
1. Change the environment and doing A no longer delivers feeling X, so actions that were moral once become less so as the environment changes (they no longer deliver feeling X, our 'moral' objective')
2. Doing A delivers feeling X in the short -term, but feeling Q in the long term (where Q is a feeling we definitely do not want). Humans apply hyperbolic discounting to desires that are in the future, to a varying degree. again this is just a brute fact, not an 'ought'. We just do apply hyperbolic discounting, like it or not.
3. Those pesky 'hundred other' desires, none of which make the slightest effort to be complimentary. We're constantly trying to balance our actions to deliver these feelings we desire despite the fact that they are not remotely complimentary.
These three factors account for all the moral variation you see in the world, different environments delivering different solutions, different levels of hyperbolic discounting and different rational solutions to competing desires. None of this changes the fact that the desires themselves are scientifically falsifiable theories, as are theories about the solutions which best meet all of them over any given time-scale.
Of course, circling back to the first part, if you don't believe in Physicalism in the first place, then all this is rubbish. If you think God made the world, then anything goes. You have to have the fundamental belief in the first place before any of this makes any sense, but personally I think everyone does. I think that's the reason why 'Scientism' is treated with such derision. people are scared it might actually be right.