There are few philosophers whose work has ranged over such vast territory as David Hume.

His writings covered everything from human nature, the mind, the self and how we gain knowledge of the world, to ethics, religion, economics, politics and history. And there are few philosophers from the 18th century who are so respected and influential to this day.

Smart kid

Born in 1711 in Edinburgh, Scotland, it was clear from an early age that Hume was uncommonly bright. So much so, that when his older brother started his studies at Edinburgh University, the young David went with him to study Latin, Greek, history, philosophy, science, and law, all at the tender age of 10!

His family fancied he might become a lawyer and guarantee them a reliable source of income. But Hume had other ideas. He quickly bored of law and found his mind drawn to other subjects.

In his own words, he found he had “an insurmountable aversion to everything but the pursuits of Philosophy and general Learning”. So, mirroring the nightmare of many parents today, he dropped law and switched over to studying philosophy.

Experience versus reason

Hume was a voracious reader and devoured every book of philosophy he could find, from the works of the ancient Greeks to Medieval thinkers to the writings of his own contemporaries. But what he found left him rather underwhelmed.

While they abounded in ruminations of logic and reason, and were filled with speculations on the divine, or espoused apparent truths derived from reason and introspection alone, he felt their musings and insights to be hollow.

This is because they were obsessed with the rarified world of reason and tended to downplay or neglect entirely the significance of our experience of the world around us. As a result, they got tied up in wild speculation and were locked in endless debates about terminology or overly abstract reasoning.

Hume also happened to live at a time of great social and intellectual transformation due to the unfolding scientific revolution. Scientists like Isaac Newton had already shown how much we can learn about the world just by carefully observing and interacting with it. Hume was determined to apply these same experimental methods to philosophy, chiefly to understanding human nature.

In his own words, he sought to “reject every system … however subtle or ingenious, which is not founded on fact and observation”. What was paramount to Hume was experience, which is why he’s known as one of the greatest proponents of “empiricism”, the idea that experience is the foundation of all knowledge.

Impressions and ideas

The atoms of experience were what Hume called “perceptions” and they came in two different flavours.

The first were “impressions”, which are just the raw experience we have when we look at the blue sky or feel a pang of hunger.

The second were “ideas”, which are the shadowy residues these impressions leave in our minds, things like the “blueness” of the sky or the memory of hunger, or purely abstract things like numbers.

Crucially, these ideas cannot simply emerge from nowhere – they must be linked to some prior impression. Even the idea of a mythical pegasus can be linked back to impressions of real wings and horses.

Hume did believe we could conceive of abstract ideas, like in logic and mathematics, but they didn’t necessarily tell us anything about the world around us. He contrasted these abstract ideas with matters of fact, which were based on experience.

In doing so, with a swift stroke, he put an end to the hypothetical speculations of past philosophers, and declared that their musings had no real value when it came to understanding the world.

He wrote:

If we take in our hand any volume; of divinity or school metaphysics, for instance; let us ask, Does it contain any abstract reasoning concerning quantity or number? No. Does it contain any experimental reasoning concerning matter of fact and existence? No. Commit it then to the flames: for it can contain nothing but sophistry and illusion.

The self and our future are in flux

Hume’s commitment to empiricism did have some troubling implications. First, he was famously sceptical about the existence of a “self” at the core of our being that makes up who we are and persists over time.

This is because when he introspected and tried to pin down the impressions such a self might leave, all he could find were individual experiences, feelings and memories.

This led Hume to conclude the self was not a single enduring thing, but rather a “bundle” of different experiences, much like a swarm of bees, with impressions and experiences drifting in and out of the mass.

He was also skeptical about things like the concept of causation and the assumption the world tomorrow will function in a similar way to the world today.

He could experience individual events first hand, but he could never directly experience the causal glue that connected them together. Thus he argued that causation was just a convenient conjecture we impose upon our experiences rather than being real.

Similarly, we believe the future will be like the past simply because that’s the way it has always been. But past experience alone doesn’t logically guarantee the future will operate in the same way. The philosophical problems he raised around these concepts are still hotly debated to this day.

Your passion rules your reason

He also argued for a somewhat radical view of morality.

Many of his predecessors believed there was a tension between emotion and reason, with the emotions causing us to behave rashly and reason enabling us to understand what we ought to do, and check our impulsive urges. To them, to be moral was above all to be rational.

Hume flipped this idea on its head. He argued reason alone was entirely impotent at motivating our behaviour. Reason, he said, is just mental computation, and all it does is help us describe and understand things. But it takes emotions – what Hume called “the passions” – to actually motivate our behaviour.

He famously stated:

“Reason is, and ought only to be the slave of the passions and can never pretend to any other office than to serve and obey them.”

The passions that mattered in terms of morality were sentiments, like sympathy, and being able to step into someone else’s shoes and experiencing what they were feeling. Reason can help us understand what we should do in order to act in a moral way, but it’s the passions that motivate us to actually act.

It turns out Hume was remarkably prescient in his understanding of our moral psychology. Recent studies have shown that Hume was on the right track when it comes to the role of the emotions in motivating moral judgements.

When we see someone do something immoral, we first experience a sense of outrage, and only after that does reason kick in to explain why we think it’s wrong. The reasons we give are often made up after the fact to justify our sense of outrage.

This is one reason why so much debate about moral matters go nowhere, as we’re all just throwing post-hoc rationalisations at each other rather than talking about the sentiments that triggered our sense of outrage.

The heretic

Hume also wrote extensively on religion, although his work in this field was considered so controversial it wasn’t published until after his death in 1776. This is because he applied his same sceptical and critical method to issues such as the immortality of the soul, and the possibility of miracles and the existence of God, among other things.

In many cases, Hume concluded that these debates were hollow and devoid of any real content relating to the way the world is. And Hume believed that these issues had great importance, particularly compared to the philosophical ideas he had previously criticised.

He wrote:

“Generally speaking, the errors in religion are dangerous; those in philosophy only ridiculous.”

As with his other arguments, these issues are still hotly debated today.

Hume is known as one of the most influential of the English language philosophers, with a clarity of thought and breadth of analysis that is both highly accessible and deeply insightful.

Reading Hume is like having one’s eyes opened and one’s complacency shattered. Hume reminds us that we are in and of the world, and we can’t descend into introspection and expect to understand the world just by thinking about it hard enough.

Rather, we have to get out into the world, observe it carefully and not allow ourselves the indulgence of believing anything to be true without first testing it against experience.

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