Suppose one person or some people say that something is true. And other people, perhaps you, are inclined to think that it is false. Should the burden of proof be on the second set of people, such as you, to prove that this idea is false? Or should the burden of proof be on those who say it is true to prove it true, by some reasoning or by some evidence?
I write this now because I heard some people, whom I know a little and whom I value, being unwilling to say they think a particular thing does not exist, because they do not have any evidence to prove it does not exist. These people do not have any belief that it does exist. That is close to the words they said themselves.
One of them wrote that, if he were to state that the thing does not exist, he would be taking the burden of proof, to prove that the thing does not exist.
I agree with both these people that there is no evidence disproving this thing’s existence. We also agree that there is no evidence in favour of it.
But I think that to say it does not exist is not taking the burden of proof. I explain this here below. It is about the huge ratio of false propositions to true propositions.
Propositions true, false, and ones whose truth we don’t know
Some propositions (statements) about the world are true, and some others are false. Also, the sum of all humans’ knowledge includes whether various propositions are true or false; and there is another set of propositions for which humans have no knowledge whether they are true or false.
How big are these 3 sets of propositions, in comparison to each other?
1. True propositions (whether humans know this or not). To be in this set, a proposition must correspond with some actual aspect of the world or part of the world. (in order to be even able to correspond, the proposition must be composed in a coherent and meaningful way).
2. False propositions (whether humans know this or not). To be in this set, a proposition must be able to correspond to some state of the world, that is, the proposition must be composed in a coherent and meaningful way. As it is not required to correspond with some actual aspect of the world or part of the world (being false, it conflicts with some aspect of the world), these propositions are less constrained. So there are a much larger number of false propositions than true propositions.
Here is a slightly different way to look at the huge ratio of false propositions to true propositions. Consider a proposition like “John is x metres tall”. The true proposition may be “John is 1.75 metres tall”. This would be true if John is indeed that size.
You can modify the true proposition by substituting another number for 1.75. Such a proposition is false. You can make many similar false propositions, “John is 1.9 metres tall”, “John is 1.5 metres tall”,….
For each true proposition there are many false propositions.
3. Propositions, that we don’t know if they are true or false. Well, for the propositions, which we do know are either true or false, there exists some way to obtain evidence about them, and some humans have worked to get that evidence.
For the propositions whose truth or falsehood we do not know, there may not be a route to obtain evidence, or there is a route but no human has done the work to get the evidence yet.
That there would be a route to get evidence is a constraint on the status of a proposition being known, while there is no such constraint on the proposition whose truth is not known.
The set of propositions, which humans do not know are true or false, is vastly greater than the combined sets of propositions which we do know are true, or false.
Of propositions whose truth or falsehood we do not know, nearly all of them are false, as follows from the reasons why the set of false propositions is many times the size of the set of true propositions. So, for any proposition for which we don’t know its truth, it is considerably more likely to be false than true.
Propositions of which we read or hear: true, false, and status unknown
Of the propositions that any reader hears or reads, the true ones are not such a tiny set compared to the false ones; and the combined set that we know to be either true or false could easily be larger that the ones with which we are familiar but do not know if they are true or false.
Why are both these ratios so different from the minuscule size of the true compared to the false and of the known compared to the unknown, as I wrote above?
Because humans are fairly rational. So, for most propositions proved to be false, people stop thinking about them; books and older people stop telling younger people about them. Similarly, people cannot sustain attention to many untested propositions which have no consequences on people (if they had some consequence, that could be evidence towards truth or falsehood, or at least would suggest a route towards a test of truth).
Where to lay the burden of Proof
A proposition, for which there is no evidence in favour, and also no evidence against, is a member of the set whose truth or falsehood we do not know.
Contrary to what may be a common perception that this set is not large, this set is enormous by comparison to the set where we know the proposition is either true or false.
Also contrary to a similar common perception that there is not a huge excess of false propositions over true propositions, a proposition whose truth or falsehood we do not know is vastly more likely to be false than true.
Suppose that, on knowing of a proposition which some other person or persons believe or claim to be true, but with no evidence in its favour, you do not decide that it is false, because you do not have evidence to prove that it is false.
Whatever are your reasons to think at least briefly about this idea, when you do not think very often about such not-proved-or-disproved propositions, this particular idea belongs in a set of propositions that is enormous when compared to the set of propositions known to be false, and even more enormous when compared to the set of propositions known to be true.
If you do not decide it is likely to be false, because you can’t prove it to be false, you would in principle be accepting as possibly true a very large number of ideas – and nearly all propositions in that set are false. You would be accepting that you carry the burden to disprove this particular idea now, but in principle you would be accepting the burden of proof for a very, very large set of propositions for which just now there is no evidence.
As an alternative to that, because the idea with no evidence in either direction has a very large chance of being false, you could say that you think it is not true. You could lay the burden of proof on any person who would say that it is true.
Peter O'Hara 