Is Determinism self-refuting?
https://academic.oup.com/mind/article-abstract/XC/357/99/996147?redirectedFrom=PDF
Have you ever heard the claim that determinism is "self-refuting" because if one is determined to believe in determinism that somehow means that we do not rationally believe in determinism?
Sir Eccles states, "this denial either presupposes free will for the deliberately chosen response in making that denial, which is a contradiction, or else it is merely the automatic response of a nervous system built by genetic coding and molded by conditioning. One does not conduct a rational argument with a being who makes the claim that all its responses are reflexes, no matter how complex and subtle the conditioning."
I really don't understand why this should undermine determinism; if we are determined to rationally come to believe X then why does it matter that we came to believe X by deterministic means?
Note: I am not arguing that determinism is correct, but I just don't understand this critique of determinism so if anyone could explain it to me that would be great. Also, if any of you have your own arguments for why Sir Eccles is correct or incorrect I would greatly appreciate reading them.
Have you ever heard the claim that determinism is "self-refuting" because if one is determined to believe in determinism that somehow means that we do not rationally believe in determinism?
Sir Eccles states, "this denial either presupposes free will for the deliberately chosen response in making that denial, which is a contradiction, or else it is merely the automatic response of a nervous system built by genetic coding and molded by conditioning. One does not conduct a rational argument with a being who makes the claim that all its responses are reflexes, no matter how complex and subtle the conditioning."
I really don't understand why this should undermine determinism; if we are determined to rationally come to believe X then why does it matter that we came to believe X by deterministic means?
Note: I am not arguing that determinism is correct, but I just don't understand this critique of determinism so if anyone could explain it to me that would be great. Also, if any of you have your own arguments for why Sir Eccles is correct or incorrect I would greatly appreciate reading them.
Comments (70)
You make a good point. All I get from the argument is that determinism is not rationally justified if determinism is true. This doesn't (obviously, to me) mean that determinism is false. Now his point may simply be that it is not rationally justified, and so (as beings invested in being rational) we ought not accept it as true.
It sounds like that word "rational" needs to be defined before we even talk about whether determinism is self refuting.
Indeed. And defining rationality pretty soon becomes philosophy's project. To determine the rational is in some sense to determine everything else. If I grant your method authority, then you do indeed give the last word on reality. Note that objectivity is authoritative for philosophy in the grand sense (for those who assume that reality can and should be determined rationally.)
*There are anti-philosophers who deny rationality/objectivity, but this is problematic if they ask to be taken as authorities.
"Rationality and determinism are incompatible. Why? Because you require free will in order to be rational. Why? Because if you lack free will, all you choices a determined i.e. determinism is true."
It appears that the conclusion is inserted into the premises of the argument.
Do I believe 2+2=4 simply because my brain is in a certain state? That seems untrue because I can reflect on the logic behind 2+2=4 and am not simply forced to believe it.
To me reevaluating and testing beliefs is the reverse of determinism.
Churchland's objection to this is that it doesn't follow that, even if determinism is true, we do not reason rationally and I tend to agree. If a person is asked for the quantity of marbles in a jar and reasons via calculus but is out by, say, five marbles from the actual quantity, I don't think it is necessarily so that this person's reasoning was irrational or non-rational. The most that can be said is that the question determined an answer of quantity, not quality of answer.
The argument that Popper makes in The Self and Its Brain (1973)* is that by committing to determinism you forfeit any claim to rationality; in particular, you cannot support your belief in determinism by a rational argument. Thus, determinism is self-undermining (not self-refuting). This argument does not provide you a reason to think that determinism is false. It only purports to show that you cannot possibly have a rational reason for believing determinism.
* The book was written in collaboration with Eccles, but they wrote two of the three parts independently, and Churchland's references in that book are to Popper's part.
Note that by determinism Popper means both causal determinism (the idea that "physical theory, together with the initial conditions prevalent at some given moment, completely determine the state of the physical universe at any other moment"), and more generally, "mechanical determinism," materialism, or physicalism - all of these terms are used interchangeably. His main challenge is to the idea of the causal closure of the physical world, or "World 1":
Popper argues that all of these "worlds" exist and causally interact with each other. (And even within each world there are still more worlds, or layers, that likewise exhibit both upwards and downwards causation.) World 2 emerged from World 1 in the course of biological evolution, and World 3 emerged from the other two. But this order of emergence does not reflect the hierarchy of causal relationships between the worlds, because once they emerge, they begin to strongly interact with each other in every direction.
As for the argument that Churchland criticizes, it proceeds from Popper's rejection of epiphenomenalism: the idea that the mental is causally inert and does not interact with the physical world - which to him means the same thing as to say that the mental is not real. And this leads him to conclude that "if epiphenomenalism is true, we cannot take seriously as a reason or argument whatever is said in its support.".
The proof of this thesis is offered in the form of a lengthy dialogue between a Physicalist and an Interactionist, but my impression is that the idea of self-defeat, declared beforehand, does not come through clearly in that dialogue. Popper once again endeavors to defend the reality and indispensability of his World 3 - the world of ideas - and once he is satisfied that he has thrashed his imaginary opponent on that point, he declares victory.
I suppose a sketch of the argument would look something like this:
1. If the physical world is causally closed (this thesis Popper variously labels as materialism, physicalism or determinism), then it follows that the world of ideas is causally inert. (Some alternatives, such as the identity thesis, are rejected in separate arguments.)
2. Take any proposition, such as 1 + 1 = 2, or indeed the proposition that affirms the truth of physicalism. To what does it owe its truth? Both the proposition and any arguments in support of its truth are abstract ideas. But the physicalist only has the physical world at her disposal to make the argument. Nor can the abstract be reduced to the physical. Thus it follows that the physicalist cannot rationally support her own position.
More later.
Great post. I like the mention of World 3. Have you looked into Husserl? Whatever 'meaning' is, it is largely objective (unbiased) and effective in whatever 'nonmeaning' is. It also occurs to me that the 'physical' is no more clearly specified than the nature of language allows. The specification of non-language or non-meaning happens within language or meaning.
Quoting SophistiCat
Indeed, that makes sense to me.
(Let me start by noting that I'm not a determinist, so my comments below are not sourced in wanting to support determinism:)
I haven't heard that claim before (or I don't recall it at least--I have a crappy memory), but it's not a good argument.
First off, whether determinism is true would have jackshit to do with whether anyone rationally believes determinism is true. Anything that anyone believes (rational or otherwise) isn't going to have any impact at all on whether determinism is true or not.
Further, all someone would have to say is that if we can't rationally believe in something just in case determinism is true (which this argument, sans other details, has to be suggesting, otherwise it's a non-sequitur), then if determinism is true, we don't rationally believe in anything (including, of course, Sir Eccles' and others' belief that determinism is false) . . . and so what? It's not as if there's a requirement in this case that we rationally believe anything.
This comment I do not understand as written, by the way: "This denial . . . presupposes free will for the deliberately chosen response in making that denial." I suppose he was just suggesting someone essentially saying, "I chose that 'determinism is true' of my own free will"? No one would say that.
Maybe Sir Eccles was simply saying that he doesn't consider anything a rational argument if one didn't freely choose to believe it, and he requires a rational argument to be persuaded that P, so he cannot be persuaded that determinism is true. Aside from that fact that that would be question-begging, he's also assuming that anyone's goal would be to persuade him that determinism is true. I don't know why anyone should care if he believes that determinism is true. (Especially not when he's set up a impossible, question-begging requirement to be persuaded.)
No, I stick with analytics; continentals make my cat-brain hurt :razz: Although the clarity of analytic philosophers can be deceptive (when it is not trivial). For example, I still don't have any clear idea of how "interactionism" is supposed to work: exactly how those worlds and levels are supposed to be affecting each other? Popper doesn't really explain.
Man, I don't remember any of that, although I can't even remember if I read that book now.
At any rate, that's problematic that Popper is conflating materialism/physicalism and determinism (in my opinion as a physicalist who isn't a determinist).
In my view, the abstract is easily "reduced" to the physical.
Arguments to the effect that determinism (and/or materialism/naturalism/physicalism) is self-defeating* abound. In The Self and Its Brain Popper cites biologist J. B. S. Haldane's argument (later retracted) from 1932: "...if materialism is true, it seems to me that we cannot know that it is true. If my opinions are the result of the chemical processes going on in my brain, they are determined by the laws of chemistry, not of logic." He traces the argument even further back, all the way to Epicurus: "He who says that all things happen of necessity cannot criticize another who says that not all things happen of necessity. For he has to admit that his saying also happened of necessity." **
* Either in the sense that it is self-contradictory, i.e. it implies its own falsity, or more commonly, in the sense that it undermines rationality, and therefore cannot be rationally justified, even if true.
** Popper acknowledges one (rather week) objection to such arguments, which he addresses, but it is not the objection that Churchland makes, contrary to what he says in his reply to her (Is Determinism Self-Refuting, 1983).
Here is C. S. Lewis, writing in 1947:
James Jordan in Determinism's Dilemma (1969) identifies and critiques a version of the argument in Kant, as well as in a few more recent writers. Here is his own emendation:
Alvin Plantinga's Evolutionary Argument Against Naturalism (EAAN) is of the same nature. It takes on the more specific claim that our cognitive faculties arose by way of natural evolution, with no supernatural guidance, but its thrust is basically the same. A similar argument was given earlier by William James. Having been revived by Plantinga, EAAN has spawned its own body of literature.
I have come across dozens more papers discussing the thesis, often in the context of the freedom of will (by those who are impressed by incompatibilist arguments).
Why isn't it obvious to people that those are horrible arguments, though?
First off, materialism doesn't entail determinism. Secondly, Haldane is just assuming that if determinism is true, then (a) knowledge isn't possible, and (b) logic isn't possible. We would at least need some sort of plausible argument for (a) and (b).
And re the Epicurus quote, obviously in that case (if determinism is true) "criticizing another who says that not all things happen of necessity" also happened of necessity. So rather that it being the case that the first guy cannot criticize the second, it would rather be that the first guy cannot NOT criticize the second.
There are similar problems with the other arguments, too, although at least Jordan's is not so conspicuously stupid.
Such a huge percentage of arguments in philosophy (not just these, not just this topic, but across the entire field in general) strike me as ridiculously bad to an extent where they suggest that the originator is rather dim-witted (albeit with a large or at least esoteric vocabulary). It's really disappointing.
Not that I'm a determinist, by the way, I'm not. But I'm not going to endorse a bad argument just because the conclusion is something I agree with. We could say "If free, rational thought guides these arguments, then that's maybe one of the better endorsements that desiring alternatives could have." ;-)
Quoting Terrapin Station
Okay, so is his argument hiding a hidden premise? Is it the case that he believes that for knowledge to be possible that one must be able to have libertarian free will?
Yes. Otherwise his comment/argument wouldn't make sense. If determinism implies that we can't know x, then one has to be saying that freedom is necessary to know x.
This is not an unusual use of the term determinism - at least it was not at that time. Nowadays determinism is most often taken to mean Laplacean causal or nomological determinism, but in the context of the freedom of will and related topics, determinism was sometimes taken to mean something else. Boyle, Grisez & Tollefsen have a nice discussion of it in Determinism, freedom, and self-referential arguments (1972). They give the following definition:
So determinism is effectively opposed to libertarianism: "explanations of human actions exhibit the appropriate inferential and nomological pattern of explanations found in physical and biological sciences," as opposed to "explanations of action form a unique type of explanation with special logical and methodological requirements distinct from those of explanations in natural science." (Richard Brandt and Jaegwon Kim, "Wants as Explanations of Actions," 1963).
As should be clear, determinism in this sense is compatible with causal indeterminism.
You are right in that Popper does not make such a clear distinction - in fact, he talks explicitly about Laplacean determinism in places. But I suspect that his thinking was motivated more by the other sense, that of explanatory determinism. Nevertheless, both he and Eccles end up betting on causal indeterminism on their quest to escape explanatory determinism - which I think occasions confusion.
To see this, suppose that we were trying to teach Physics to an unruly student who refused to abide by our experimental physics conventions in his application of the equations. Since we can only provide him with a finite list of commands, he can always find a way to abide by our stated instructions and yet violate our intentions to produce nonsensical and lawless results.
Our Physical laws are therefore only meaningful relative to our obedience to the experimental conventions that we use to confirm them. Hence they are partially representative of our choice to conform to physics culture.
That's not determinism being self-refuting, i.e. denying or undermining itself through its own entailments - that's just you denying determinism. Not the same thing, and not what the topic is about.
Right. So a determinist cannot interpret his opponent as asserting a contrary epistemological position. Therefore the determinist cannot interpret his own position as making an epistemological claim.
My view is that any assertion of a necessary consequence is an active imperative as opposed to a passive description of an objective matter of fact. Therefore i agree with the above argument that determinism isn't an epistemological position.
Quoting sime
I can't see how you are getting this from the quoted snippet. I think you are just reading into it your own thoughts (which I don't claim to understand).
By his very belief in universal determinism, the determinist, if he is consistent, cannot interpret his opponent's sentence " I possess free will" to be an actual claim to possess an objective property. This is because if universal determinism is true then the only objective meaning the determinist can ascribe in his opponent's sentences are the physical causes that precipitated them. Therefore the determinist must understand his opponent's sentences to be trivially and necessarily correct in an epistemological sense whatever those sentences are, and to be 'wrongable' only in the conventional sense of disagreeing with the linguistic convention adopted by the determinist.
This paradoxically implies that the thesis of universal determinism makes no substantial objective claims either, by failure to oppose a substantial counter-thesis.
To my understanding, our practical usage of the verb "to determine" which always relates a 'determiner' and a thing being determined, points to the natural way of dissolving the problem of free will.
This sounds somewhat like Popper's argument that says that physicalist (let's call it that to avoid confusion) ontology is too impoverished. But a physicalist need not limit herself to just the "objective" language of physical causes. At least I haven't yet seen a persuasive argument to that effect.
A computer can be programmed to make rational decisions without giving it the property of free will, so I'm not convinced the conclusion is in the premises. Then it seems to boil down to whether it is the rationality encoded in the software or the atoms in the hardware that are causing the decision.
There seems to be different conceptions of determinism at play: one based on the closure of physics, the other seems to admit other forces such as reason. I don't understand the latter conception.
I think that Popper and Eccles really mean the sort of material determinism that takes the universe from one state to the next. If you admit the causal power of "animals" and "design" you are already stepping outside material determinism, into a situation where abstractions are causal. I think the two conceptions are distinct, and this could be the cause of some confusion.
No. The confusion arises out of making them distinct. Abstractions are causal. They cause us to behave in certain ways when they are in or mind. How did those words, "animals" and "design" get on the screen in your post if the abstractions, "animals" and "design" aren't causal?
It makes no sense distinguish between, "material" or "abstractions" when they both are causal. That is why I didn't use those terms in my explanation. They are unnecessary and cause more problems than they solve. Dualism is a false dichotomy. Monism is the truth.
What laws do abstractions obey? We know the material is bound by the laws of physics, so presumably abstractions have similar constraints. What are they?
I copied your words, as a matter of fact.
If you insist on games, the initial conditions at the Big Bang plus the laws of physics compelled me to write those words, and all the words I have ever written, obviously.
That is the argument: there is only one substance, and that physics is closed.
Yes, there is only matter and the laws of physics. Your "animals" and "design" are not real.
As far as I know determinism is an argued position. I think it's an argument from analogy. Everything around us seems to follow the laws of nature and that implies the past determines the present. Why should we be an exception?
The onus, it seems to me, of proving anything to the contrary lies with freewill enthusiasts.
There's a "good" reason to believe in determinism but I don't see any good counterarguments.
Quantum mechanics, I believe, suggests a non-determnistic subatomic world. Our minds could be quantum machines and, ergo, capable of freewill.
As for Eccles he ignores the above argument.
We know about the past because we use the present, and the laws of physics to infer it. That's how we discovered the big-band, galaxy formation, and how elements were made etc. The laws of physics work just as well backwards in time.
So, I'm not sure the laws of physics are sufficient to make the claim that there exists an inescapable causal chain from the past to the future, as, due to their time-symmetry, these laws don't really describe such a thing.
Didn't Hume write something pertinent to this, about his inability to discover "cause" in nature?
Quoting TheMadFool
Perhaps the initial conditions at the big-bang will lead, via inexorable causal chain, to such a refutation.
One interesting thing that I'd like your opinion on is our ability to imagine alternatives.
We get into a situation and we, rather instinctively, come up with options. We make a graded list of alternatives. People could construe this as frewill at play.
However, we make our choices according to constraints that apply during our decisions. I mean we choose the best option first. If that is unavailable then we choose option 2 and so on.
So, the entire alternatives thinking and acting process is driven by constraints that are beyond our control.
I guess what I'm getting at is that to entertain options indicates an intelligent mind but not necessarily freewill.
Isn't this just Eccles's argument? If you are a determinist, then there really is no such thing as an argument that satisfies a rational agent, there are only atoms bouncing off each other. If you believe that arguments, proofs, reason, and rational agents exist, then how can you be a determinist?
Quoting TheMadFool
I confess I'm slightly confused by the idea that choices and alternatives are real, yet somehow determinism holds. i.e. I don't understand Compatibilism.
My understanding of "determinism" (i.e. the current conception of determinism) is isomorphic witht eh block-universe of relativity. The future already exists.
This makes no sense to me (and by the way I'm ignoring issues with "claims possessing objective properties" and the idea of objective meaning).
Two immediate problems with your comment spring to mind.
One, determinism doesn't necessarily imply physicalism (and neither does physicalism imply determinism for that matter).
Two, why couldn't the person believe that meaning is physical?
Then we don't agree. You keep using this term, "matter". I don't know what that is. I'd say that your distinction between "matter" and "ideas" is not real.
"Matter" = "chunks of stuff" basically. Like a piece of wood, leather, a pebble, etc.
Being rational doesn't mean we have freewill. Does it? We can program computers to be rational. In fact that's all they can be.
What are we left with? Emotions? That we've realized is hardwired. We don't choose to be sad or happy. Emotions are less within our conscious control than rationality.
What say you?
Let's look at Eccle's argument. If the world is deterministic then what we believe isn't within our control. The argument assumes that rationality is not possible in a deterministic world. But we have computers - perfect rational machines - and they don't have free will.
You are reprising A.J. Ayer's argument in The Concept of a Person (1963):
Note however that this argument only shows that causal determination does not preclude rationality. The argument that determinism is self-defeating usually makes a weaker claim: that there is no necessary connection between physical causality, which produces what we take to be beliefs and other mental states, and the attributes of truth, logic, reason, etc. that we would like to claim for our beliefs. If the physical world is causally closed, then truth, logic, reason, and other abstract things cannot have an effect on it. And if so, then any correlation between the two realms is either fortuitous or due to some inexplicable preexisting harmony. So the argument goes...
Because . . . of an assmption that those things are not part of the physical world? Otherwise, the connection there would need to be explained better.
If logic, reason, etc. are physical things, then they're part of the causal closure in that case, and could indeed have an effect.
If you claim that rational processes exist, that reason is a feature of reality, that reason is causal, then have you not already stepped out of material determinism? Something other than the initial conditions and laws of physics causes the present to be the way it is.
Once you admit the causal power of abstractions, then you have let the cat out of the bag.
Right, that would be the identity thesis: the abstract, or the mental just is the physical, or somehow supervene on the physical (and then it's just the matter of "naturalizing" them if you wish to demonstrate the specific connection).
Well, the identity thesis for someone who accepts determinism, yes. ;-)
Computers are neither rational nor irrational; they neither follow reasoned arguments nor fail to follow them, they merely execute instructions.
Suppose you have two computers, A and B; you program A to follow modus ponens, and you program B to follow the fallacy of affirming the consequent. A will appear to you to be rational and B will appear to be irrational, but in fact both A and B are just blindly following the procedure you programmed them with.
The conept of rationality simply does not apply to computers. Rationality requires understanding, and computers don't understand, they merely obey.
But although I disagree with your argument, I agree with your conclusion: being rational does not mean we have free will. Being rational is a matter of understanding the logical connections between ideas; free will (which personally I do not believe exists) is not a matter of understanding, but of being able to influence events.
But, the output of the computer depends on the instructions. The instructions are real and causal, despite them being independent of their physical instantiation. A program in C will cause the same effect as a program written in Fortran, despite them being physically different. A program stored on punched cards will have the same effect as one stored on a hard disc.
It seems to me, that if you permit the existence of real causal abstractions - like instructions, knowledge, reason - then the future can't be determined by the laws of physics alone.
Quoting Herg
This is the claim that an artificial general intelligence is impossible. And it is just a claim.
Quoting Herg
What is the constraint that allows certain abstractions to exist e.g. rational agents, but prevents others from existing, e.g. rational agents with free will?
Quoting SophistiCat
But isn't that assuming dualism of some kind? Reason has causal import but reason isn't an immaterial thing as of necessity. Right?
Well, the argument doesn't explicitly assume any metaphysical stance on the nature of reason; it seeks to challenge determinists (in this context: those who maintain that our actions and thought processes are due only to physical causes) on their own ground.
The underlying dispute seems to be whether the determinist can consistently assert an objective distinction between reasons and causes. Such a distinction could only be objective if the truth-maker of a reason is transcendent of the proximal causes of it's assertion such that the reason isn't merely said to be true or false by linguistic convention.
How can the determinist consistently assert that "determinism is true" is neither made true by linguistic convention, nor by the proximal causes that provoked him to say it?
We don't need to know what matter is made from, all we need to know is how it behaves, how it interacts, and why. Of course, we do know most of the basic constituents of the universe, and we do know that these constituents are quanta of various types of field.
We also know, ideas aren't made of energy.
We explain how matter behaves as a result of what it is made of - tiny particles called atoms.
Quoting InisWe do? What are ideas made of? If you don't know, then how can you say that you know they're not made of energy? and how do they establish causal relationships with matter?
Science has progressed a fair way beyond that.
Quoting Harry Hindu
How does energy establish a causal relationship with atoms?
Quoting Inis
I don't believe in the existence of abstractions, only in the existence of concrete particulars.
Quoting Inis
And the opposite claim is also just a claim.
I think what we are really talking about here is consciousness. An entity which is not conscious cannot be said to understand anything, because to understand is to have the subjective experience of understanding. And since we don't know what it is about brains that produces consciousness, we don't know whether a machine can be conscious, and therefore whether a machine can understand.
Quoting Inis
As I said, I don't believe in the existence of abstractions.
All if them? Including "rationality", "consciousness", "understanding", "subjective experience"?
Quoting Inis
I think these are just properties of concrete objects. It's the objects of which they are the properties that are involved in causation, not the properties themselves.
None of these properties, that you claim concrete objects can possess, is mentioned in the laws of physics. In fact, "causality" itself isn't mentioned in the laws of physics either.
What I am curious about is whether these properties such as consciousness are real, or whether they are just epiphenomena, or convenient names we give to collections of atoms?
My suspicion is that these properties are now epiphenomenal, but were not always so. Consider the pain you feel when you burn your finger. Scientists tell us that you snatch your finger away before you feel the pain, suggesting that the pain is epiphenomenal; but why have we evolved to feel the pain, if it serves no causal function? I think perhaps pain was causal millions of years ago, but then animals evolved a faster response system that by-passes the pain, leaving it as an epiphenomenon.
Even if these properties are epiphenomena, that doesn't make them unreal. We don't imagine that we feel pain when we burn ourselves, we really do feel pain.
So suppose, as you say, that in our evolutionary past pain (qua mental state) served a causal function. Does that mean then that the neurophysiological states that realized this mental state were epiphenomenal? How would that work?
Wiktionary gives two definitions of 'epiphenomenon':
"1. Being of secondary consequence to a causal chain of processes, but playing no causal role in the process of interest.
2. (philosophy, psychology) Of or pertaining to a mental process that occurs only as an incidental effect of electrical or chemical activity in the brain or nervous system."
I've been using 'epiphenomenal' in the first sense, not the second, which I suppose is unusual in a philosophy discussion; I probably should have made this clear. I'm suggesting that pain originally was not epiphenomenal in the first sense, but now is. My conjecture assumes no particular view of the mind-brain relation, it's merely a suggestion about how one brain process may have supplanted another because it offered a selective advantage.
If pain has never been causal throughout evolution, then I can see no reason (i) why it should have evolved at all, or (ii) why it should be so unpleasant (if the subjective sensation is not what causes us to withdraw the finger and never has been, the sensation could just as well have been extremely pleasant, since pleasant or unpleasant, it would have made no difference).
The rarity of congenital analgesia shows that (a) it is possible to be injured without feeling pain, and (b) being injured without feeling pain has been largely selected against in evolution. Consequently there is a need to explain how evolution has been able to select in favour of pain, and if pain has always been epiphenomenal, this selection seems impossible.
If anyone with a greater knowledge of evolutionary physiology than I possess can give reasons to doubt my conjecture, I would be very interested.
How does that challenge work?
I believe thinking is unique but is it so in reality or is it simply our inability to explain it (in physical terms) that makes it so?
At best, pain signals us about some adverse environmental circumstances or a bodily disorder, so that we attend to this situation and deal with it. But of such situations those in which unconscious reflexes (like yanking a finger out of a fire) are adequate and sufficient are relatively few.
Why is it so damn unpleasant? And why do we feel it, even when there is nothing we can reasonably do about its cause (without the amenities provided by our modern civilization, which evolution could not have anticipated)? Well, evolution is primarily a satisficing process, rather than an optimizing one: it often settles on a good-enough solution. It must be that occasional bouts of misery did not impose as high a cost on reproductive success as the alternatives that were available at the time.
Besides, though I am no more an expert in this area than you are, surely unconscious reactions would have evolved much earlier than anything like pain? Even organisms without any central nervous system have those.
Quoting TheMadFool
Well, different people have posed it somewhat differently, and you'll have to read their arguments to understand. Though sometimes simply, even flippantly stated (like Sir Eccles' quote in the OP), it's not so simple really. In my opinion, James Jordan's statement that I quoted in this post is one of the most cogent.