Skip to main content

THE 'YOU CAN'T PROVE IT EITHER WAY" MOVE A bit from draft for my DK book Companion Guide to Philosophy

(this was cut down in published version)

Reasonableness comes in degrees (B heading)

INTRO: Beliefs can be more or less reasonable. There is, if you like, a scale of reasonableness on which beliefs may be located. Unfortunately, that reasonableness is a matter of degree is often overlooked. It’s sometimes assumed that if neither a belief A, nor its denial B, are conclusively “proved”, then the two beliefs must be more or less equally reasonable or unreasonable. As we will see, this assumption is false.

MAIN TEXT. Some beliefs are very reasonable indeed. It’s reasonable for me to believe that the orange on the table in front of me exists, because I can see it there. It’s also reasonable for me to believe that the tree outside my house still exists, because it was there when I last looked, and I have no reason to suppose anyone has removed it in the meantime. And it is reasonable for me to believe that Japan exists, despite the fact that I have never actually been there. I possess an enormous amount of evidence that Japan exists, and hardly any evidence to suggest it doesn’t.
            Of course, despite being highly reasonable, these beliefs could still conceivably turn out to be false. Perhaps the orange I seem to see before me is an hallucination. Perhaps the tree in my garden has secretly been removed by pranksters. In the film The Truman Show, there is a conspiracy to dupe the main character into thinking he is living his life out in the real world when in fact everything around him is part of a carefully managed TV set. Even those he believes to be his closest relatives are, in truth, merely actors. Perhaps I am the unwitting victim of a similar complex conspiracy to make me believe Japan exists when in fact it doesn’t.
            So let’s acknowledge I might be mistaken in holding these beliefs. Certainly, I cannot prove them beyond all doubt. But of course, this is not to say these beliefs aren’t eminently reasonable. They clearly are. They lie towards the top of the scale of reasonableness.
            At the bottom of the scale lies the belief that faeries and goblins exist. This is a very unreasonable thing to believe. There’s no good evidence these tiny folk exist and plenty of evidence that they are fictional. Still, it does remain a remote possibility that these fairy-tale folk exist. We can’t prove beyond all doubt that they don’t.
            Around the middle of the scale of reasonableness lie beliefs which are neither highly reasonable nor highly unreasonable. Take the belief that there are intelligent life forms living somewhere out there in the universe. True, we have no direct evidence of any such extra-terrestrial intelligence. On the other hand, we know that intelligent life has evolved on this planet, and we also know that there are countless other similar planets out there. So it’s not particularly improbable that there is intelligence out there somewhere.
Beliefs can change their position on this scale over time. A few decades ago, belief in electrons was fairly reasonable. Given the additional scientific evidence that’s since been discovered, it is now very reasonable. At one time belief that the world is flat was perhaps not so unreasonable. It’s now very unreasonable indeed.
The scale may also vary from one person to the next. It’s very reasonable for me to believe there is an orange on the table in front of me, because I can see it there. Perhaps it’s not quite so reasonable for you to believe there’s an orange there. After all, you can’t see the orange. You simply have to take my word for it.
Of course, it’s contentious where some beliefs lie. Take belief in the existence of God, for example. Some consider belief God is no more reasonable than belief in fairies. Others believe it is fairly reasonable – at least as reasonable as, say, belief in extra-terrestrial intelligence. Those who claim to have had direct experience of God, or who think miracles and so on constitute fairly good evidence that God exists, may place belief fairly high up on the scale (even while acknowledging that their belief is not “proved”).

The “You can’t prove it either way” move

Having set up the scale of reasonableness, let’s now look at a common mistake people make when assessing the reasonableness of a belief.
Sometimes, when someone has been given very good grounds for supposing a belief B belief is false, they respond by saying “But you can’t prove B is false, can you? B might be true!” They think this shows belief B is still pretty reasonable – perhaps even as reasonable as the belief that B is false.
Here is an example. Suppose you have just provided Ted with excellent grounds for supposing his belief that there are fairies at the bottom of the garden is false. Ted responds “But you can’t prove there are no faeries down there, can you?”, as if that showed that his belief is, after all, pretty reasonable – perhaps even as reasonable as yours.  Now perhaps you can’t prove beyond all doubt that there are no faeries. It’s just possible that you’re mistaken. Still, it’s hardly likely, given the evidence. On the available evidence, Ted’s belief remains downright silly.
Here’s a philosophical example. Even if we cannot conclusively prove either that God does exist or that he doesn’t, it doesn’t follow that the belief that God exists is just as reasonable or unreasonable as the belief that he doesn’t. It might still be the case that there are very good grounds for supposing God exists, and little reason to suppose he doesn’t. In which case it is far more reasonable to believe in God than it is to deny his existence. Conversely, there might be powerful evidence God doesn’t exist, and little reason to suppose he does. In which case atheism may be far more reasonable. We should not allow the fact that neither belief can be conclusively proved to obscure the fact that one belief might not be far more reasonable than the other.
Unfortunately, theists sometimes respond to atheist arguments by pointing out the atheist has not conclusively proved there is no God, as if that showed belief in God must be fairly reasonable after all. Actually, even if the atheist can’t conclusively prove there is no God, they might still succeed in showing that belief in God is very unreasonable indeed – perhaps even as unreasonable as belief in fairies.
Pointing out the absence of “proof” against a belief does not show that the belief is, after all, at least fairly reasonable.

IMAGE OF A RECTANGLE, LEFT HALF RED MIDDLE HALF WHITE AND RIGHT HALF GREEN. IN LEFT-HAND RED HALF PUT “DISPROVED” IN RIGHT HAND GREEN HALF, PUT “PROVED” IN MIDDLE BOX PUT “NEITHER PROVED NOR DISPROVED”. Caption: Rather than arranging beliefs on the scale of reasonableness, we might sort them instead into the three boxes “proved, “disproved” and “neither proved nor disproved”. We may then lose sight of the fact that the beliefs in the middle box may still differ dramatically in terms of their reasonableness.

The ambiguity of “proved” People often talk about a belief being “proved”, “not proved”, “disproved”, and so on. But what does “proved” mean here? It can mean a variety of things, including:

Proved beyond all possible doubt
Proved beyond reasonable doubt
Shown to be certain
Shown to be almost certainly true
Shown to be very probably true

Notice that people often talk of “scientific proof” despite the fact that most, perhaps all, scientific claims are open to at least some doubt.
When using the term “prove” it is important to be clear what you mean. Take for example, the claim that we cannot “prove” God exists. It might be true we can’t “prove” beyond all possible doubt God exists. But then perhaps we can still “prove” God exists in the sense we can still show his existence to be extremely probable, or to be at least beyond reasonable doubt. Conversely, even if we can’t “prove” beyond all doubt God does not exist, it doesn’t follow that we can’t show his existence to be extremely improbable. We should not allow loose use of the word “proved” to obscure these facts.

IMAGE OF GOD. Caption: Where should we place “God exists” on the scale of reasonableness? Indeed, should belief in God appear on the scale at all (but if it doesn’t appear on the scale, why not?)

NB. Nothing I say here should be taken to commit me to evidentialism - the view that a belief is reasonably held only if it is supported by evidence. Evidentialism is probably false. See here.


StewE17 said…
An article to refer to when debating with people who have not thought about what they mean when they talk about proving and disproving things. So many times in the comments below articles some dimwit will post "You can't prove God doesn't exist!": the inference being of course that God therefore must exist.

But please can we have the images and captions for this blog? e.g.



Miles Rind said…
I'm wondering about that rectangle that's half red, half white, and half green. It sounds like a diagram of Manbearpig.

On the main subject, you may want to address the question of what makes a belief reasonable or unreasonable. People who hold unreasonable beliefs do not, as a rule, regard them as unreasonable; so trying to use the distinction between what can be disproved and what, though not disprovable, is nonetheless unreasonable, is of limited effectiveness in disputation with them.

I'm glad to see you noting the variety of meanings of "prove." I have encountered people who dismiss the notion of scientific proof, saying that nothing can be proved outside of mathematics and logic. But clearly, the term "prove" has a highly specific meaning in those fields, viz., "deductively valid demonstration from axioms." That this is not the common meaning of the term outside of those fields is shown by the use of "prove" and "proof" in forensic contexts. E.g., nobody who speaks of a "burden of proof" is talking about mathematical demonstration.
Anonymous said…

I think the graphic would be more clear if it went from black to white with linear changes in shades of grey in the middle section. Alternately (if in a full color edition of the publication), you could pick any two frequencies (publishers may be able to suggest the most eye-catching colors)in the spectrum and and show a linear progression between them.

I don't know if you're writing this for an academic or a general audience publication, but if it is for the general public, I'd leave out the footnote on the difference between Evidentialism and Reliabilism. As someone who is not a philosopher, the difference appears like mere semantics to me (given the average reader may be more philosophically savvy than I am).

I would also expand the section beginning with, "The ambiguity of “proved.”" Most of us needed that explained somewhere along the line. How is a mathematical proof different from "proving" something in a court of law, or in history, or science, or better yet everyday experience (when you turn the key, do why do you believe the automobile will start?)?

Other than those couple of personal preference things, I think it's great! I have no training in philosophy, but it's clearly written. I could read it, understand it, and come up with questions based on it.
= MJA said…
How To Build A Real Castle

If you are going to build a castle in the sky, believe it or not, One must start with a foundation made of truth, a single absolute. And if I may, I'll place the first stone right of just here: =
Philip Rand said…
"Of course, it’s contentious where some beliefs lie. Take belief in "infinity", for example...Mathematicians claim to have had direct experience of "infinity", think mathematical calculations and so on constitute fairly good evidence that "infinity" exists, so place this belief fairly high up on the scale (even while acknowledging that their belief in "infinity" is not “proved”).
Unknown said…
stephen law, i need to talk to you !!!
Ophelia Benson said…
I think I spotted a typo, a meaning-reversing one, so worth pointing out.

"We should not allow the fact that neither belief can be conclusively proved to obscure the fact that one belief might not be far more reasonable than the other."

I have a strong and reasonable belief that you meant to say "that one belief might be far more reasonable than the other" - in other words, that that second "not" doesn't belong there.
Philip Rand said…
What exactly does "more reasonable" mean exactly?

I mean, which statement is "more reasonable"?

1/ The Earth existed 300,000 years ago.

2/ The Earth existed 5 minutes ago.

I can see plenty of "reasons" existing for the former proposition.

But, sure as hell can't see any "reasoning" required for the latter...

So which proposition is more reasonable?
Martin said…
What exactly does "more reasonable" mean exactly?

I mean, which statement is "more reasonable"?

1/ The Earth existed 300,000 years ago.

2/ The Earth existed 5 minutes ago.

I can see plenty of "reasons" existing for the former proposition.

But, sure as hell can't see any "reasoning" required for the latter...

So which proposition is more reasonable?

Your questions intrigued me, so I am going to have a go at answering them.

I'll start with 2/

As far as I know, the Earth existed 5 minutes ago. I also know that practically everyone I ask if this is true will agree with me. I know that there are a tiny percentage of people who lack short term memory and so may not be able to answer the question. Because I have a rough understanding of why lacking short term memory may adversely affect these people's answers, I think I can discount such answers. I therefore think it is highly reasonable to accept that the Earth existed 5 minutes ago.

Now I'll tackle 1/

I have no personal experience of the Earth existing 300,000 years ago. I'm not a scientist, but I do have a worldview which accepts that the scientific method is valid. The scientific consensus is that the Earth existed 300,000 years ago, with little controversy. I therefore believe it is reasonable to believe the Earth existed 300,000 years ago. I understand that the scientific consensus can change from time to time, that my reasoning relies upon me interpreting information supplied by scientists, and it is unlikely I'll ever be in a position to confirm this fact for myself. I therefore call my position reasonable, but not highly reasonable.

According to my perspective, 2/ is more reasonable than 1/.

There's nothing in Stephen's post to say that others may not differ in what they view as more or less reasonable. A Young Earth Creationist would look at 1/, realise it is not consistent with Biblical literalism, and reject 1/ as unreasonable. I think they would still be able to agree with me that 2/ is highly reasonable. Furthermore I believe that they would agree with Stephen's central point that beliefs are more or less reasonable. We would both believe that 2/ is more reasonable than 1/, although clearly our reasoning to reach this conclusion will differ.
Philip Rand said…

What "reasons" make you come to the conclusion that the earth existed 5 minutes ago?

That you can see it?

That you can feel it?

Would you say that these are "reasonable" grounds for such a belief?

I mean, seeing is non-cognitive, feeling is where is the cognitive "reasoning" that determines whether the earth existed 5 minutes ago? The fact that your senses are telling you this?

Is this "reasonable"? i.e. is any reasoning used to come to this conclusion?

You wrote it yourself..."personal experience" experience (i.e. the senses) reasonable?

This is not the same way you would reason the earth existed 300,000 years ago? Because here, you are using "reasoning"...
Philip Rand said…
Thing is,

The earth existing 5 minutes ago is a certainty without any possibility of error...whereas the other proposition has a possibility of error...

So, in fact the earth existing 5 minutes ago is a certainty reached without any reasoning (i.e. cognition involved)...

Therefore, can you say that this proposition is more reasonable?
Martin said…
I cannot reach the conclusion that the Earth existed 5 minutes ago without using my memory, and applying that memory to an understanding of what "5 minutes ago" means. Both memory and understanding are parts of cognition, so I would say I am doing some reasoning to get to that conclusion.

It may not seem very hard, but no child is born with an innate understanding of "5 minutes ago". Therefore it has to be learnt, and to use it cognition must used.

Philip Rand said…
An infant seconds out of its mother's womb can suckle it's mother's breast for milk...

No cognition is involved...nor does the infant use "reason" that it's mother's breast exists.
Martin said…
Are you conceding my points and introducing a new topic (which would be highly reasonable of you), or are you changing the subject because you don't wish to concede the points (which would be highly unreasonable on your part)?
Philip Rand said…

How exactly is memory related to "reasoning"?

Isn't memory for humans simply a gauge measurement of the past?

A squirrel has a far superior memory to humans when it comes to remembering where it has stored its thousands of nuts for the winter...does a squirrel use reason to find it's food hoards?

When you use memory to determine the earth existed 5 minutes ago...aren't you simply extrapolating from the "now" that you experience and what your senses are telling you?

And isn't this simply an illusionary exercise?

I mean, are you really using "reason" when you all ready are certain that the earth existed 5 minutes ago?

So where is the reasoning? I mean, you are not in any doubt that the earth did not exist 5 minutes ago...even before the question was asked...

When you determine if the earth existed 300,000 years your proof centred on your senses?
Martin said…
Philip, you ask a lot of questions, but you are not very good at answering them. I'll do just the one for now.

How exactly is memory related to "reasoning"?

They are both part of cognition.

If you can answer my question honestly I'll come back to your other points.
Philip Rand said…
Well Martin

What question am I supposed to answer honestly Martin?

I am not good at responding to pachyglossal apodyopsis...sorry...

Retrospective memory is cognitive...Familiar memory is pre-cognitive...

It is Familiar memory that informs your Retrospective memory that gives you the illusion that you are using "reason" when you attempt to answer the question concerning the existence of the Earth five minutes ago.

A simple technique to uncover these types of propositions is to use negatives, i.e.

"I don't know the Earth existed 5 minutes ago."

Just as equivalent would be:

"I don't know I have a head."

When you look at the negative propositions like this, they are simply non-sensical...which usually means the positive of the proposition are also non-sensical.

Philip Rand said…
You know Dr Law...

Is it really "reasonable" to believe that the orange on your table exists?

I mean, say you walk into the room containing the table and on it is an orange...

You see the orange...the thing is, do you "recognise" the orange on the table, i.e does this thought occur to you? Is this recognition cognitive...

I don't think it is...and therefore is not a "reasonable" belief...

You may doubt your sense of the orange but you can't doubt your belief in the orange.
Philip Rand said…
Actually, I should be clearer (funny how a phrase can create confusion)...

So where I wrote:

"You may doubt your sense of the orange but you can't doubt your belief in the orange"

It should read:

Your sense of the orange you see may be wrong but you can't doubt your belief in seeing the orange.

Ah...that is better...clarity...

Popular posts from this blog

What is Humanism?

What is Humanism? “Humanism” is a word that has had and continues to have a number of meanings. The focus here is on kind of atheistic world-view espoused by those who organize and campaign under that banner in the UK and abroad. We should acknowledge that there remain other uses of term. In one of the loosest senses of the expression, a “Humanist” is someone whose world-view gives special importance to human concerns, values and dignity. If that is what a Humanist is, then of course most of us qualify as Humanists, including many religious theists. But the fact remains that, around the world, those who organize under the label “Humanism” tend to sign up to a narrower, atheistic view. What does Humanism, understood in this narrower way, involve? The boundaries of the concept remain somewhat vague and ambiguous. However, most of those who organize under the banner of Humanism would accept the following minimal seven-point characterization of their world-view.


(Published in Faith and Philosophy 2011. Volume 28, Issue 2, April 2011. Stephen Law. Pages 129-151) EVIDENCE, MIRACLES AND THE EXISTENCE OF JESUS Stephen Law Abstract The vast majority of Biblical historians believe there is evidence sufficient to place Jesus’ existence beyond reasonable doubt. Many believe the New Testament documents alone suffice firmly to establish Jesus as an actual, historical figure. I question these views. In particular, I argue (i) that the three most popular criteria by which various non-miraculous New Testament claims made about Jesus are supposedly corroborated are not sufficient, either singly or jointly, to place his existence beyond reasonable doubt, and (ii) that a prima facie plausible principle concerning how evidence should be assessed – a principle I call the contamination principle – entails that, given the large proportion of uncorroborated miracle claims made about Jesus in the New Testament documents, we should, in the absence of indepen

Plantinga's Evolutionary Argument Against Naturalism refuted

Here's my central criticism of Plantinga's Evolutionary Argument Against Naturalism (EAAN). It's novel and was published in Analysis last year. Here's the gist. Plantinga argues that if naturalism and evolution are true, then semantic epiphenomenalism is very probably true - that's to say, the content of our beliefs does not causally impinge on our behaviour. And if semantic properties such as having such-and-such content or being true cannot causally impinge on behaviour, then they cannot be selected for by unguided evolution. Plantinga's argument requires, crucially, that there be no conceptual links between belief content and behaviour of a sort that it's actually very plausible to suppose exist (note that to suppose there are such conceptual links is not necessarily to suppose that content can be exhaustively captured in terms of behaviour or functional role, etc. in the way logical behaviourists or functionalists suppose). It turns o