Evidence, m’lud

Part of a series which began with Fake news and the ethics of belief.

Evidence was a 1922 silent film directed by George Archainbaud and starring Elaine Hammerstein.

This article is not about this Evidence however but about evidence as something that may or may not support a belief.

Last time we gave examples of descriptive and prescriptive beliefs in relation to Clifford’s evidence principle (‘CP’) and suggested more limited wording (‘EP1’) which excluded prescriptive beliefs:

[CP] It is wrong always, everywhere, and for anyone, to believe anything upon insufficient evidence.

[EP1] It is wrong to believe anything, within the category of descriptive belief, on insufficient evidence.

We want to start looking at whether a prescriptive belief is even the kind of thing you could have evidence for. But to do that we first need to ask what the relationship is between evidence and  a belief.

Here is a fairly formal working definition of ‘evidence’:

A statement s counts as evidence for a belief that p if s is true and s provides objective reasons for thinking p is true or is likely to be true

For most purposes we could say that evidence for a belief is something which is likely to be true if the belief is true and likely to be false if the belief is false.

First take a descriptive belief:

[I believe that] I was born after the Second World War

My birth certificate gives my year of birth as 1950, which is after 1945.

Had it said 1930 that would count as evidence against my belief about being born after WWII. That seems fairly straightforward.

In a case like this we should typically be able to see the relationship between evidence and belief in ‘ordinary life’.

But even here the relationship would rest on background beliefs like ‘The Second World War ended in 1945’, which, ultimately, we might just have to take on trust. When we start spelling out these background beliefs they all appear to be descriptive beliefs.

Berlin Reichstag 3 June 1945

Our second descriptive belief was:

[I believe that] Water is a compound of hydrogen and oxygen

This would be less apparent in ordinary life. If we had the technical wherewithal we might try burning a quantity of hydrogen in a quantity of oxygen and see what we get, and how much. But again the relationship between this evidence and this belief would rely on background descriptive beliefs including scientific theory about closed systems and the conservation of mass.

A perhaps more problematic case is:

[I believe that] There is a God

This is clearly a descriptive rather than prescriptive belief, but there seems a remote chance of anything like universal agreement over what would constitute evidence for it.

Some people might for example say the evidence for God’s existence is all around us and is overwhelming. The whole of creation is evidence that God exists.

Others might say this rests on some highly dubious background beliefs, namely that the universe, or ‘creation’, was something created, and had a creator.

Detail from Sistine Chapel ceiling

But this shouldn’t worry us right now. The principle still holds that a descriptive belief can be supported by evidence, even if we may argue whether that evidence is really there or is what we think it is, or want it to be.

Read on.

© Chris Lawrence 2021