John Locke
The 17th century saw the beginnings of one of the most important epistemological debates in the history of philosophy, that ran well into the 18th – between empiricists and rationalists. The empiricists were mainly British and Irish – e.g. John Locke (1632-1704), George Berkeley (1685-1753) and David Hume (1711-1776), the rationalists mainly continental – e.g. René Descartes (1596-1650), Baruch Spinoza (1632-1677) and Gottfried Wilhelm Leibniz (1646-1716).
George Berkeley
The empiricist position was that knowledge is a posteriori (‘from later’ – you have to go out and get it): that is, it comes from experience – for example through sensory perception and/or scientific experimentation. We have to investigate cause and effect. Just because a sick person takes a pill and then they get better, it doesn’t mean that the pill was the cause of their recovery. To find out with more certainty (but not complete certainty) you’d need reproducible scientific testing of hypotheses, using well-designed experiments, statistical analysis of the data collected, after which, specialists in your field need to check it to see if your methods were valid, and your conclusions coherent (peer-review).
The rationalist position was that knowledge is a priori (‘from earlier’ – you already have it if you think about it) – that is, it comes from reason, for example through mathematics or logic. The mind is fitted with rational faculties, and if we follow them, we will get to the truth. Reason, operating within the laws of logic, can attain knowledge of truths that owe nothing to sense experience.
David Hume
From a common-sense perspective, it’s difficult not to dismiss the debate, and to say that some problems suit empiricism and some rationalism. To quote a previously-mentioned example, if there are two concentric circles, you don’t need to do any measurements to find out if the inner circle is smaller than the outer circle – logic is enough; however, you do need measurement if you want to know how much smaller it is.
And Hume, although an empiricist, is famous for saying that (and I paraphrase): ‘you can’t get an ought from an is’, which means that however much we know about the universe, it doesn’t tell us anything about how to act. We can’t learn what we should do from observation or experimentation. Why is murder wrong? Because we don’t like it. Empiricism is employed to turn metaphysics into physics, but can’t help us when it comes to morals or ethics.
Baruch Spinoza
But it’s not as simple as that (it never is with philosophy). Rationalists state that without the mental infrastructure provided by reason, none of our experiences would make sense anyway – we would just perceive a mass of sensory data that didn’t add to our understanding of the universe. For example, if you had no ‘innate’ or a priori knowledge, and a brick was thrown through a window, you would just have an experience of a flying brick, the sound of smashing glass, and a lack of window – just shards of glass lying on the floor. But you wouldn’t have an understanding that the brick caused the broken window – not without an innate knowledge of cause and effect.
So do mathematics and reason provide more certainty than the evidence of our senses? Abstract mathematics seems to represent the real universe perfectly, as Pythagoras said it did, but it’s not time to ignore metaphysics in favour of mathematics yet. E=mc² is such a pure, clean equation that appears to represent reality perfectly, and Einstein predicted that light would be bent by gravity using just mathematics, several years before it was confirmed with observation. But there’s no rational reason why mathematics should represent reality. That’s still a mystery.
Gottfried Wilhelm Leibniz
Also, the empirical position that the only acceptable explanations are causal explanations appears to be in trouble since the discovery, via quantum physics, that sub-atomic particles don’t seem to operate in terms of cause and effect. But what do we mere humans know? A computer can be programmed to do random things, and to someone who’d never seen a computer, it would seem that those things had no causes. In the same way, quantum activity may have perfectly obvious causes to a cleverer species than humans. What I would advise however, is to take with a pinch of salt any metaphysical explanation that involves quantum physics, because as Richard Feynman said: “If you think you understand quantum mechanics, you don’t understand quantum mechanics”.
It was left to Kant to reconcile empiricism and rationalism.
Next: Enlightenment.