What is this thing called validity

11 Jul 2017

We all hold a variety of beliefs about climate change. The Earth is warming; The Earth isn’t warming; The Earth is warming and human activity is the cause; The Earth is warming but human activity isn’t the cause; We are causing the Earth to warm and we have a moral imperative to stop it; We are causing the Earth to warm but we have no obligations to act.

And there are many reasons why we might hold these beliefs. I read about it in a book; I saw it on Fox News; I heard it from a man with PhD wearing a lab coat; Believing it makes me feel good. Psychologists, sociologists, and cognative scientists can furnish us with a range of explainations about why we believe these things but a more interesting questions is whether we should believe them.

One obvious and somewhat tautological reason for holding a belief is because it is true. While it might sometimes be more comfortable to embrace cognative dissonance or socially productive to except a noble lie, believing something is true just because it is true seems self evident. In fact, it would be both a contradiction and extremely difficult to knowingly believe a falsehood was true.

The problem of course, is that it can be very difficult to independently know which beliefs are true and which are not. Some beliefs can be justified by reference to observation and experience. Others can be justified by reference to their source or testimony. But most of all, beliefs can be justified by reason and this is especially important when we are trying to convince others to accept our belief.

The way we can use beliefs to justify other beliefs, and why we should be confident in this, is actually quite straight forward. Beliefs are simply truth claims about the world we live in. “Over 90% of climate scientists believe in anthropogenic climate change” (objectively true), “New York City is the capital of New York state” (stipulatively false), “it will rain tomorrow” (unknowable today), “Salted peanut butter ice-cream is better than pastacio lime flavour” (subjectively true).

Every truth claim or proposition semantically entails some other proposition. The claim that “Today is Monday” entails the claim that “Today isn’t Tuesday” (or any other day of the week for that matter) simply because of the meaning of the claim. In a similar way, it is possible to organise propositions about claims we know to be true in such a way that together, they collectively entail some other claim that we didn’t but now know to be true. This is what we call an argument.

An example here will help. If I know the following two claims are true:

  1. All birds have feathers,
  2. My pet doesn’t have feathers.

Then together, these propositions exclude the claim that “My pet is a bird”. Given the meaning of these claims, they can’t all be true at the same time. So if the first two claims (the premises) are true, then the last claim can’t be true. And if it is impossible for “My pet is a bird” to be true, then I infer with certainly that the opposite “My pet isn’t a bird” must be true (assuming of course that the premises are in fact true).

This relationship between propositional claims within an argument, where the meaning of the premises (were they true) excludes the possibility of the conclusion being true is what we call validity. And validity is a key element in the application of reason.

Using reason as a criterion of belief justification has a number of advantages. Firstly, it means that the medium through which we communicate becomes less significant. An immersive film or inspirational oratory can have powerful rhetorical impact, stroking our emotions and motivating us to act. Psychologists have demonstrated how cognative biases like the halo effect mean that physical stature, dress, gender, tone, and tenor make us unconcious prone to believing claims based not on what was said but on who said them. Appeals to reason by contrast, permit us to accept the content of what was said, not how it was said or who said it.