Prove It! How We Know What We Know, Part 3

Welcome back! If you’ve been following this series on how we know what we know, you know that so far we’ve looked at David Hume and Immanuel Kant to help us fight against the popular, but misguided, thought that we can only be sure about things we can see and touch, hear and smell for ourselves. 

Today we’ll look at why Thomas Reid thinks that idea smells fishy.

Thomas Reid

This whole discussion from Hume to Kant is nice to understand if we can, but there is a convenient way of avoiding it: Reid, representing the common-sense tradition in philosophy, recognizes a bundle of X-beliefs: the existence of the world outside the mind, the fact that the past is not a fiction, the existence of other minds, the fact that testimony is a source of knowledge, the reliability of the senses, the reliability of reason, the uniformity of nature, and more.

Reid also realizes that Hume is right about the importance of X beliefs. And he says we can know them. Hume said we believe them by a right and useful instinct; Reid agrees, but he also thinks that that instinct is a source of knowledge.

One nice thing about Reid is that the last thing I mentioned about Kant—Kant proves that X beliefs are prerequisites for perception—can be easily integrated into the Reidian account of knowledge.

The big thing to remember about the difference between Kant and Hume, on the one hand, and Reid, on the other, is that on the Reidian account we get to say that we know X beliefs are true of the world outside the mind!

But how do we know them? A good question.  And along comes Alvin Plantinga a couple of centuries later to finish the job in his book Warrant and Proper Function.  Although Reid did not explain in much detail how an instinct can be a source of knowledge, Plantinga explains how these instincts are also sufficient for giving X beliefs a degree of warrant.

  • When I have an X belief, my belief in it is produced by cognitive faculties (which ground the aforementioned instincts) aimed at the production of true beliefs;
  • these faculties are reliable;
  • they are functioning properly;
  • and they are functioning in the right environment.

And a belief that is warranted is a belief that can be known.

“Now Let Us Hear the Conclusion of the Matter”

So here are the three main options we’ve looked at:

  1. Hard Empiricism, inspired by Hume: Knowledge of the world outside the mind comes from, and only from, experience. Since there are X-beliefs, there is no such thing as knowledge of the world outside the mind.
  2. Kantian Soft Empiricism: Knowledge of the world outside the mind comes from, and only from, experience. Since there are X beliefs, there is no real knowledge of the world outside the mind. We canhave knowledge from experience, but really it’s knowledge of the world inside the mind.
  3. Common-sense Soft Empiricism: Knowledge of the world outside the mind is possible. It depends on X-beliefs. Our trust in X beliefs comes from instincts that are sufficient to give our beliefs a degree of warrant. So we can know X beliefs, and we can gain knowledge from experience as a result.

And why does this matter?

It’s easy—indeed, it’s downright fashionable—to say that religious or ethical or metaphysical beliefs are by definition irrational because they are not justified by experience.  Only a belief justified by science can be rational; only a belief justified by science can be known—thus say some critics.

Now, as I’ve already mentioned, we don’t really have to grant that no religious, ethical, or metaphysical beliefs are justified by experience.  However, even if we did grant that, so what?  Knowledge does not come only from experience.  In order to know anything about the world from experience we must presume at least these beliefs that don’t come from experience, but make it possible to learn from experience:

  • that the world outside the mind exists;
  • that that world is three-dimensional;
  • that it is in time;
  • that the past is not a fiction;
  • and that our five senses have access to the world.

And for science to give us any knowledge we also have to presume, at a minimum:

  • that there are other minds;
  • that their testimony (i.e., the testimony of a scientist) is a source of knowledge;
  • that there is a uniformity of nature or else that reason, either inductive or (if Karl Popper is right) deductive, is reliable.

That is why this matters: Many an argument leveled against religious or moral tradition has appealed to a false premise.  So what if some principle is not justified by experience? That, in itself, proves nothing. Nothing is justified by experience unless something is not.