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The Evidentialist Principle

August 10, 2011

Time to continue my look at evidentialism. So far, I’ve tried to show that we are at least coherent in thinking that there is such a thing as an ethics of belief and how we could define “belief”. The central theme of this post will be to suggest evidentialism as the correct ethics of belief, hopefully with some justification. The next post (probably after a holiday-induced delay) will try to defend evidentialism from possible attack.

In a 2008 paper Allen Wood provides what I think is probably the best formulation of evidentialism that I have seen:

Apportion the strength of your belief to the evidence; believe only what is justified by the evidence, and believe it to the full extent, but only to the extent, that it is justified by the evidence. (Wood: 9)

This is less extreme than the call by Clifford for anyone, at anytime, and anywhere, to only belief anything on sufficient evidence. The principle above gives room for partial belief in the face of only weak evidence, which is important. One thing that is important to note is that this definition doesn’t restrict evidentialism to a narrow, empirical form of “evidence”. It allows whatever form of justification we decide is epistemically acceptable. I take evidence here to mean empirical evidence, logical arguments and suitable testimony (more on this in the next post).

Now, I’m going to take it as given that what we care about in whatever process it is that we use to form beliefs is that the process leads us to believe things that are true, or at least more likely true than not (in which case we may only hold a partial belief, but anyway…). This makes sense from our definition of belief – if I am going to assert something as true (which I will if I believe it), this doesn’t make sense unless I actually think it is in fact true.

This leads us to the first point in favour of evidentialism: it is natural. Consider an exchange in which someone else tells me that they believe P. Put in the form of our working definition, they assert that P is true. In any natural situation we are going to believe that they do in fact hold P to be true, and moreover that they have reasons for thinking this is the case. We work on an assumption that other people aren’t bullshitting, that their beliefs are aimed at truth, and we naturally consider evidence as the path to this truth. Without this, we wouldn’t be able to exchange much of the information that passes between us everyday. When I ask a stranger for directions, I don’t assume they’re making them up, I assume they have sufficient reasons to give me the specific directions that they give.

A second point is found by considering the role of evidence. It is fairly uncontentious to say that a belief supported by evidence is more likely to be true than a belief unsupported by evidence. Having evidence allows us to increase the probability of a belief being true. Given the desire to hold true beliefs over false beliefs, this speaks in favour of evidentialism. A rival theory would have to be able to play some substitute role in increasing the probability, and I don’t yet know what else other than evidence could do this.

What other reasons could we have for thinking that evidentialism might be true? Wood breaks down reasons into “self-regarding” and “other-regarding”.

Self-regarding grounds for evidentialism are premised on

the idea that each of us has good reason to regard ourselves as having a certain value, a value entitling us to self-respect. (Wood: 18)

Thus our self-respect, or dignity, makes ethical demands on how we think and act. Part of this is that we shouldn’t let other people do our thinking for us when we are capable of doing the thinking ourselves. So, whilst I might have to accept testimony from someone about the obscure workings of some part of algebraic topology say, I shouldn’t accept on faith testimony that I am more than capable of thinking through myself. If I’m presented with a belief and asked to accept it on faith, I should ask myself what evidence there is for it. Only when the testimony comes from a source known to reliably cause true belief should I lower this standard, because that in itself counts as evidence.

Another self-regarding ground is wishful thinking. We shouldn’t believe something in the absence of evidence (or in the face of evidence) just because we wish it were true. As Wood points out:

We naturally wish we knew many things we can’t know – such as what (if anything) becomes of us after we die, or whether there is a benevolent power secretly watching over us, or perhaps the ultimate fate, after we are gone, of some great historical cause to which we have devoted ourselves. It is depressing and frightening to realize that you can never know these things; it is pleasant and consoling to have a belief about them… (Wood: 18)

But if you think that beliefs formed on the basis of insufficient evidence can make such beliefs reasonable, he further points out that :

You should be ashamed to deal with your human predicament in this cowardly way. (Wood: 19)

To form beliefs based on wishful thinking is to lose our dignity as freethinking individuals.

Other-regarding grounds are those that involve others. Firstly, what we believe can and does affect others. If any effects are caused by beliefs with insufficient evidence, surely we should be morally culpable for these beliefs in a way that is not seen if beliefs are formed according to the principle of evidentialism? Further, by even putting ourselves into a situation where others may be affected by our beliefs, or even just asked to agree (or disagree) with our beliefs, we do not respect their dignity as rational, self-respecting moral agents if we do not confront them with our most honest appraisal of the evidence, if we ask instead that they accept our beliefs on faith.

…we owe it to others, simply as fellow human beings and partners in the collective rational search for truth, to offer them, in the give and take of communication, what is best in oursleves and our unique perspective. (Wood: 21)

In short, we owe them beliefs based on evidence, that have reasons lending them weight, that may in fact be true.

So there we have it: my attempt at a (short) case for evidentialism. Of course, some will naturally think that whilst the principle of evidentialism espoused above may be true some or most of the time, there are occasions when faith is necessary or desirable. What would it take to convince me that this is the case?

  1. You would have to be able to tell me what beliefs it is that are exempt from the moral demand for evidence.
  2. You would have to be able to show that we can in fact know these beliefs to be true (or likely true) despite there being no evidence.
  3. Finally, you would need to show how this belief fits into a moral framework that allows for self- and other-regarding grounds for morality.
I think that’s a pretty tall order. No defence of an epistemology based on faith that I’ve seen has come close to being able to justify itself. I think I’ll stick to evidentialism.


Wood, A (2008), The duty to believe according to the evidence, International Journal for Philosophy of Religion 63, 7-24.

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