Prove It! How We Know What We Know

People sometimes object to religious belief on the grounds that it’s not empirical—and all knowledge, they insist, comes from experience. I’ve written before at TTC on the premise that religious belief is not empirical. It’s not a true premise.

But there’s something else wrong with this objection: Not all knowledge comes from experience. The very nature of empirical knowledge proves that knowledge does not come from experience alone—not if we actually have any knowledge, that is.

There are certain beliefs that are necessary if we are going to learn anything about the world from experience, but which are not themselves justified by experience.  In order to know anything empirically we have to know some things on a non-empirical basis.

In other words, there are principles that are fundamental to empirical reasoning. Since we have to have such principles already in place in order to learn from experience, they cannot themselves be learned from experience.

Let’s call any such principle an “X belief.”  A number of important philosophers have looked into X beliefs.  In this three-part series, we’ll look at three of them: David Hume, Immanuel Kant, and Thomas Reid. 

First up: David Hume.

Hume thinks a belief can only be known if it is either known from experience or is a “relation of ideas,” i.e. a tautology like “Two and two make four.” And everything we know about the world outside the mind is known from experience.

But to know anything about the world from experience we must presume something that is not known from experience, and is not a tautology—i.e., an X belief. Hume considers three candidates for X beliefs in his Enquiry Concerning Human Understanding.

  • Cause and effect: You have to presume that these are real, or else you can’t ever reason to any conclusions in science—such as that gravity causes things to fall towards the center of the earth.
  • Induction: This is the principle that we can learn about things we have not experienced from what we have experienced; you can’t, for example, posit that gravity effects all things without induction because we haven’t experienced all falling objects.
  • The uniformity of nature: This is the principle that things in nature always act according to the same laws of physics. How can science posit any generalized laws without presuming that the whole of nature always acts the same way it was acting when those scientists observed it?

So these beliefs are necessary to know anything much in science. But can they be known empirically? Hume, if I understand him rightly, discovers the following about those beliefs:

  • Causality can be known from experience, if you presume that induction works and if you have enough experiences to induct from.
  • Induction might be justified by the uniformity of nature, or perhaps vice versa.
  • However, one of the two—either induction or the uniformity of nature—necessarily remains unjustified.

So we’re left with at least one X belief: not causality, but one of the other two. All our knowledge by experience has at its foundation a belief that is unknowable. That means we can’t really have any real knowledge about the world outside the mind.  When we believe something (say, the conclusions of science) because we believe something else (an X belief), we have to know the latter in order to be able to know the former.

But we must accept all three of these beliefs. We just have to realize that we believe them by habit or instinct, not on the basis of reasoning.

Thus says Hume.  Stay tuned for Part 2, where we’ll discuss Immanuel Kant, and how Kant builds on Hume’s observations of X beliefs.  Later, in Part 3, we’ll look at Thomas Reid.