A Hume Contradiction

When society embraces Hume's definition of morality, it inevitably ends up breaking Hume's Law.

David Hume was a highly influential Scottish Enlightenment philosopher. His broad legacy includes his definition of morality, and the law that bears his name, also known as the is-ought problem. I find the contradiction in these ideas illuminating to understand how laws change when customs do.

Hume was an empiricist. One of his ideas was that reason doesn’t drive morality, but that emotion, passions and sentiment do. Perhaps his most famous contribution is the is-ought problem, commonly known as Hume’s Law. Hume originally wondered why those who document moral systems are prone to going from facts or descriptive statements – how things are – to prescriptions, or how things should be, with no rational process behind this jump. In simple terms, Hume’s Law says that one shouldn’t derive an “ought” from an “is”. In other words, descriptions shouldn’t automatically imply prescriptions.

Breaking Hume’s Law is a kind of logical fallacy. Whenever a fact is used to justify a commandment with no logical arguments entailing it, we witness a naturalistic fallacy. For example, if I were to say, “Reproduction occurs through sex. Therefore, people should only have sex to make babies,” I would be violating Hume’s Law. Though I start with an accurate fact – reproduction does occur through sex – there is no logical progression connecting that descriptive statement to the prescriptive commandment.

Other fallacies closely related to Hume’s Law are the appeal to nature and the moralistic fallacy. In an appeal to nature, something observed in nature is turned into a prescription. The opposite is a moralistic fallacy, where I describe and justify the way things are based on my belief of what’s right. In other words, from an “ought” I seek to enforce an “is.” A more specific type of moralistic fallacy is assuming that something is moral just because it’s legal. Slavery, for example, was legal in what today is Canada until 1833. That doesn’t mean that slavery is morally right, although that was the law and perhaps even the sentiment at that time.

Adopt Hume’s Moral Definition, Break Hume’s Law

But here’s the interesting irony: following Hume’s definition of morality almost inevitably results in breaking Hume’s Law. How so? Societies can have a carefully argued and selected set of fixed morals, such as a Constitution interpreted in the spirit the original writers meant. Or, they can have a shifting standard based on the sentiment of the moment. When it’s the latter, moral standards change over time. It’s not that people say, “This is wrong, but I’ll do it anyway.” More likely I think they say, “There really is nothing wrong with this. We need to change our stance on this. We should be able to do it without judgement, remorse or legal consequences.”

This can engender a naturalistic fallacy: a demand that laws change to accommodate the new reality. Some of these changes are supported by somewhat logical or reasonable arguments. But often things get to a point where people just say, “We must get with the times! We need to be on the right side of history! That needs to happen because it’s 2021!” In other words – it is. It ought to be.

And once the new standard is encoded into law, the naturalistic fallacy engenders the moralistic fallacy: “It’s the law. It’s a closed topic, a done deal. Society has moved on from this.”

Here’s just one of many examples of this process. On October 17 2018, Canada became the second country in the world, after Uruguay, to legalize cannabis. The federal government’s reasons to do this were: to dismantle the black market, which is estimated to pour 7 billion dollars into organized crime every year; to keep cannabis out of underage youth’s hands; and to protect the health of cannabis users by regulating the product’s quality.

Those were the overt reasons. And you could say that there also was an argument to be made against the excessively negative consequences of criminal prosecutions from possessing and using cannabis, particularly in racialized communities. However, underpinning all of this was a Hume Law violation: “people will use cannabis no matter what we do. Might as well legalize it.” So much so that other jurisdictions actually expect a tax income windfall from legalizing cannabis. Thankfully, that wasn’t a prominent theme for the Liberal government, because the jury is still out on how effective has legalization been on its goals, which makes the underpinning fallacies especially troublesome. The more logical arguments didn’t quite play out, but the naturalistic and the moralistic fallacies remain strong.

It all starts with choosing a relativistic moral standard instead of an absolute one. Mistakes inevitably follow. And as I see this unfolding today, I can’t help wondering what will the 21st century equivalent of legalizing slavery be. On what will future generations look back on us with scorn and shame?

This article is an edited extract of the “Morality, Customs, Laws and Hume’s Law podcast episode transcript.

Published: April 28, 2021