On one side of the English Channel you had the British Empiricists and on the other side you had the European Rationalists.

Empiricism and Rationalism are contrasting epistemological positions, which is to say, they have different beliefs about the origins of knowledge. The divergence between the two camps dates to Descartes’s Discourse on the Method where the French philosopher questioned the certainty of his beliefs and asked how it was that he knew anything — this is the investigation that culminated in his famous statement cogito ergo sum “I think therefore I am”.

Descartes’s work set the fire ants among the intellectuals of Europe. It agitated and stirred the philosophers to a new paradigm. The question emerged: how do we know anything? What is the basis of knowledge? And with that, a chain of epistemological questioning was set in motion that had never been so directly considered before.

In answer to the question two camps emerged: the Rationalists and the Empiricists. Descartes pioneered the Rationalist movement. In the Discourse he reasons that sensory experience is unreliable. How do I know that I am sitting at this table right now? Might I not be in my bed dreaming that this is happening? With this insight, Descartes sees that sensory experience cannot be relied on and so he says we must seek elsewhere for certainty. Ultimately Descartes finds that we can rely only on reason for knowledge and we can rely only on our minds and from there he builds his theory of knowledge.

In contrast to this, the Empiricists say that sensory experience is the only source of knowledge. The term Empiricism derives from the Ancient Greek word ἐμπειρία, (empeiria), which comes from the same etymological root as the Latin word experientia. It is from these words that we have derived our words experience and experiment.

In this article we are going to explore Empirical school of thought — often called British Empiricism because its three major philosophers came from the British Isles. We are going to look at how Empiricism developed in the writings of an Englishman an Irishman and a Scotsman— John Locke, George Berkeley and David Hume.

John Locke

The first major Empiricist in this post-Cartesian tradition was the philosopher John Locke. Locke was a radical empiricist and in opposition to Descartes, he argued that sensory experience was the only source of knowledge. Locke argued that we are born as a tabula rasa — a blank slate (or in Locke’s language a white paper). By this he meant that we are born as completely empty vessels and through sense experience our knowledge of the world is built up. We have no knowledge except that which comes through experience.

Simple Ideas and Complex Ideas

For Locke, our abstract ideas do not come from a Platonic realm of Forms but are composed out of the building blocks of reality. He distinguishes between simple ideas and complex ideas. Simple ideas are the things we experience imminently through our senses. So we develop the idea of a table from our experience of tables; we develop our ideas of tall and small from our sensory experience of small and tall things.

These are the simple ideas. The complex ideas are things like space, unity and relations between things like parent and child or cause and effect. These complex ideas are developed out of simple ideas by reflection. The simple ideas emerge from sensation; the complex ideas emerge from reflection on this sensation.

This is Locke’s explanation about the origins and development of knowledge. He also agrees with Descartes that sensory experience isn’t reliable. But unlike Descartes, Locke sees a baby in the bathwater of sensory experience whereas Descartes just throws the whole thing out because it’s not fully reliable.

Primary and Secondary Qualities

To tackle this unreliability of sensory data, Locke draws a distinction between primary and secondary qualities.

Let’s say you have a jug of wine. The primary qualities of this jug are its weight, its shape, its size and so on. According to Locke these are the qualities that belong to the actual object.

Then there are the secondary qualities. Is it hot or is cold? Depending on whether you’re in Siberia or the Sahara, the same jug of wine might appear to be warm or cold. The same goes for taste. If you are a sommelier then the wine may be delicious whereas if you had a few bad experiences with wine as a teenager then maybe it won’t. The point is that these secondary qualities can change depending on the time and the person. It might be the exact same jug of wine but its secondary qualities are different.

So what Locke did was distinguish between the primary qualities of an object — its weight, its form and its extension (i.e. its height depth and width)—and the secondary qualities of an object — its taste, smell, texture, feeling and so on. The first set of qualities are present in the objects themselves whereas the second set are present in the mind of the perceiver; they are our experience of the object rather than the object itself.

With this distinction we can see what is actually in the object itself and what is our projection on it. With the benefit of hindsight it’s also staggering to think of how important this empiricist worldview was for the development of science. By distinguishing between primary and secondary qualities we separate our experience of the object from the idea of the object in itself. The quest to understand these primary qualities of objects is a cornerstone of the scientific project.

George Berkeley

George Berkeley was an Anglican bishop from this wonderful island of Ireland. He was the next great empiricist after Locke. And it’s with Berkeley, that empiricism takes a bizarre twist. He takes the profoundly materialist philosophy of materialism to an extreme where it becomes paradoxically antimaterialist. This vein of thought is now known as Subjective Idealism.

Locke had rested secure in the knowledge that while secondary qualities were unreliable, at least we had our primary qualities. But Berkeley came along and started pulling at the threads of this certainty.

Locke had said that things like extension and form were primary qualities that were not qualities of the mind like taste and colour but qualities of the objects themselves. But Berkeley questions this: if you look at a cow up close its extension appears to be one size but if you look at it from a distance it is smaller. So which cow is the correct cow? The one that is close or the one that is far away?

So with that, Berkeley says that there is no way of separating primary and secondary qualities. They are always tied up in our experience of them. We can’t say which of the perspectives of the cow is correct —the one that is close or the one that is far away. And so we don’t actually know anything about the external world. We only have our perceptions of it. Berkeley takes this a step further.

If a tree falls in the forest

Berkeley is the source of that old philosophical conundrum — if a tree falls in the forest and there’s nobody around to see it then does the tree exist? Well, the Irish philosopher says, since things are reliant on perception for their existence, it is questionable. Without being perceived, the tree does not exist at all.

In fact, the only thing that exists are the perceivers. Matter is an illusion; this is where Berkeley’s famous dictum esse est percipi —to be is to be perceived — comes in. Only that which is perceived exists; existence itself is perception. And so the only reality are the perceivers and if you take them out of the equation the whole thing collapses. Close your eyes and the trees are gone; go to sleep and you cease to exist.

This is the problem that Berkeley runs into — if things are not being perceived then how do they continue to exist? And Berkeley gets around this the same way Descartes builds back from his Cogito — he invokes God. God, according to Berkeley, is the great perceiver. God is constantly watching constantly keeping an eye on things and keeping everything perceived and thus in existence.

Berkeley felt that he had gotten out of his bind by bringing God in as the great perceiver. But as our next philosopher David Hume points out, there is a hidden pitfall in Berkeley’s thought.

As Hume points out, Berkeley’s position is inconsistent. He goes so far as to doubt the material world of perceptions but he doesn’t doubt the spiritual world of perceptions. That is to say, he doubts that matter is something which exists when we stop perceiving it, yet he fails to apply the same standard of doubt to the existence of other perceivers. Why does the doubt stop at our perceptions of matter? Since we only know others through perception should we not also admit the possibility that other people are also mere figments of our perception? Thus Berkeley’s philosophy, consistently applied leads into the quicksands of skepticism and solipsism.

David Hume

David Hume was Scottish philosopher who was notorious in his own time for his views. He carved out a living as a public intellectual and, because of his sharp mind and his affable personality, he was a favourite guest at dinner parties.

Arthur Schopenhauer thought highly of him writing that

“In every page of David Hume, there is more to be learned than from Hegel‘s, Herbart‘s and Schleiermacher‘s complete philosophical works.” (The World As Will And Idea: 3 vols in 1. p. 721)

Hume’s Fork: Matters of Fact and Relations of Ideas

Hume is most famous for his distinction between two categories of human knowledge: matters of fact and relations of ideas. This distinction has come to be known as Hume’s Fork and it is a critical moment in the history of Western philosophy.

The relations of ideas category contains things like mathematical and logical propositions — for example the square of the hypotenuse equalling the sum of the squares of the two sides. These types of truths were called analytic truths by Immanuel Kant — who was greatly influenced by Hume saying that he “interrupted my dogmatic slumber”.

The matters of fact on the other hand were items of knowledge that relied on any observation of the world such as the sun’s rising in the east. These types of truths Kant called synthetic truths.

In turn Hume says that both of these types of knowledge are derived from our impressions. These impressions can be of two sorts — sensation and reflection. That is to say, Hume recognises an extraverted sensation — i.e. impressions arriving through the five senses so things like red, round and robin — and introverted sensation — i.e. inward impressions like desire and fear.

It’s all impressions

Hume’s radical move was to say that all of our ideas are derived from these impressions. There was no transcendent source of our ideas as the Rationalists believed. If you examined any idea closely enough you’ll be able to find its constituent impressions.

So if you take the idea of a unicorn or Hume’s example of the gold mountain what you have is the combination of two separate impressions to form something new. In the case of the unicorn it’s a horse and a horn; in the case of the gold mountain it’s our impressions of gold and mountains.

Hume has taken Locke’s argument of the tabula rasa and he has made a theory of meaning out of it. He says that for any idea to have meaning it must be grounded in an impression. Those that aren’t are meaningless. He says that:

“When we entertain, therefore, any suspicion that a philosophical term is employed without any meaning or idea (as is but too frequent), we need but enquire, from what impression is that supposed idea derived? And if it be impossible to assign any, this will serve to confirm our suspicion. By bringing ideas into so clear a light we may reasonably hope to remove all dispute, which may arise, concerning their nature and reality.”

—David Hume, An Enquiry Concerning Human Understanding

Farewell to God

And of course when you apply this theory of meaning to the idea of God the results are controversial. If you have the idea of an omnipotent divinity but you’ve never had any impression of something that is omnipotent or divine then your idea is meaningless. Most of religion and philosophy go the same way for Hume.

This went down like a lead balloon in Hume’s time. In the other early modern philosophers you can see the flirtation with atheism but always followed by the pulling back from the cavernous void as if they were afraid of the audacity of their own conclusions. We see Descartes do this after the Cogito and Berkeley do this in his invocation of God as the great Perceiver.

But Hume publicly doubted the existence of God. On his deathbed, crowds of people gathered outside his home in the Scottish capital Edinburgh, curious to see if he would repent his wayward ways in the face of death. But they were disappointed. On the contrary one of his final acts was to plan for the publication of his most anti-religious writing after his death; these were writings that even he felt were too controversial to appear in print while he was alive.

With Hume, Empiricism reached a dramatic conclusion in his moderate scepticism. We could know analytic truths by definition but the synthetic truths could never be certain in their knowledge. Sure, the sun has risen every day in the east but it is a leap to say that it will rise in the same place tomorrow. To believe so is to fall into an inductive fallacy. Until the discovery of Australia, every swan that a Westerner had seen was white. It seemed safe to assume that all swans were white but then came Australia and the Black Swan.

After Hume there was Immanuel Kant who brought an end to the Empirical/Rationalist divergence, by synthesising the two. From Rationalism he took the idea that we can have knowledge of significant truths a priori i.e. without experience while rejecting the idea that we can have a priori metaphysical knowledge about the nature of things in themselves. From the Empiricists Kant took the idea that knowledge is essentially knowledge of experience but he rejects the idea that we can’t learn any necessary truths about experience. With this synthesis, Kant reconciles the divergence and leaves Hume as the last of the Empiricists.