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What Is Causality, Actually? Explained Slowly (For Sleep) – Transcript
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- Aristotle proposed a framework consisting of four causes to explain why things happen, including material, formal, efficient, and final causes.
- David Hume argued that we never perceive a true causal connection, only constant conjunctions and temporal sequences.
- Judea Pearl developed structural causal models and the do-operator to provide a rigorous mathematical foundation for causal inference.
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So, here's something to think about as you're lying there getting comfortable, letting the day sort of drain away. You already know the answer to this question. In a way, you've known it since you were very small. If you push a glass off the edge of a table, it falls.
It hits the floor, it breaks. You pushed it and then it broke. The pushing caused the breaking. simple, obvious, the kind of thing a 2-year-old understands without anyone having to explain it. But here's the thing. If I asked you to tell me precisely, rigorously, in a way that would hold up under real scrutiny,
what do you actually mean when you say one thing caused another? What is that invisible thread between the push and the shatter? What makes it different from two things that just happen to occur one after the other?
Well, that question has haunted some of the sharpest minds in human history. And it turns out it's one of the deepest, most slippery, most quietly important questions you can ask. Not just in philosophy, in medicine, in engineering, in law, in the design of every algorithm that recommends what you watch or buy.
in the way we build bridges and test drugs and predict the weather and try to understand why economies crash causality. What is it actually?
Let's start way back. And I mean way back because people have been chewing on this for a very long time. And the earliest thinkers who left us written records were already wrestling with it in surprisingly sophisticated ways.
Around 2400 years ago in Athens, a man named Aristotle sat down. Well, probably stood actually. He liked to walk while he taught, pacing through the covered walkways of the lysum with his students trailing behind him. And he tried to lay out a complete framework for understanding why things happen.
Why does a statue exist? Not just what it's made of, but why it has the shape it has, who made it, and what purpose it serves. Aristotle didn't think there was just one kind of cause. He thought there were four, and he gave them names that we still use today, though the meanings have shifted a bit over the centuries.
The first he called the material cause. That's the stuff something is made from. The bronze of the statue, the wood of the table, the bricks of the house. It's the raw substrate, the ingredients.
Simple enough. The second was the formal cause, which is the pattern or design, the blueprint if you like. The shape that makes a lump of bronze into a statue of Athena rather than just a lump of bronze. It's the arrangement, the structure, the form.
The third was the efficient cause. And this is the one closest to what you and I usually mean when we say cause in everyday life. It's the agent, the thing that does the work, the sculptor who chips away at the marble, the carpenter who hammers the nail, the push that sends the glass over the edge. It's the thing that makes something happen. And
the fourth, and this is the one that feels strangest to modern ears, was the final cause, the purpose, the reason the statue was made in the first place, to honor a god, to decorate a temple, to win a competition.
Aristotle thought purpose was woven into the fabric of causation itself. things happen not just because something pushed them, but because they're moving towards some end, some goal. Now, you might be thinking, "That last one sounds a bit odd." and you'd be in good company because over the next 2,000 years that fourth cause, the final cause, the idea
of purpose baked into nature would become one of the most controversial ideas in the history of thought. But we'll come back to that. What matters right now is that Aristotle was doing something genuinely remarkable. He was trying to be systematic about a question that most people just take for granted. He was saying, "Look, when you ask why, you might actually be asking
four different questions at once, and you need to untangle them if you want a clear answer." That's a powerful insight. And in a way, the entire history of thinking about causality is a long winding conversation about which of those four causes really matter, which ones we can do without, and whether Aristotle missed anything.
For a long time, centuries really, Aristotle's framework dominated through the Roman period, through the medieval world, through the great Islamic scholars who preserved and extended Greek philosophy while Europe was busy with other things. Thinkers like Avashenna working in Persia around the year 1000 and Avarois in Islamic Spain a
century or so later both engaged deeply with Aristotle's causal framework refining it debating it integrating it with theology and medicine and astronomy. When Aristotle's works were translated back into Latin and rediscovered by European scholars in the 12th and 13th centuries, his four causes became the backbone of how universities
taught natural philosophy. Thomas Aquinus, the great medieval theologian, built enormous intellectual structures on Arisilian causation, using it to argue for the existence of God. The idea being that every effect must have a cause. And if you trace the chain of causes back far enough, you must arrive at a first cause, an uncaused cause, and
that's God. The argument is elegant. It's also, as we'll see, built on assumptions about causality that would later come under very serious fire. But let's stay in that medieval world for just a moment longer because something interesting was happening even then. Not everyone was satisfied with Aristotle.
There were cracks appearing small ones in the edges of the framework. One of the most fascinating early challenges came from a group of Islamic theologians called the Asherites and particularly from a thinker named Al Gazali who was working in Baghdad and other cities around the late 11th century.
Al Gazali made an argument that sounds almost shockingly modern. He said essentially that when you see fire touch cotton and the cotton burns, you assume the fire caused the burning. But how do you actually know that? All you've really observed is that the fire touched the cotton and then the cotton burned.
You've seen two events in sequence. But the connection between them, the causal link itself, that's something you're adding. You don't see causation, you see sequence, you see correlation.
And Al Gazali argued that the real cause of everything was God's will moment to moment. And that what we call natural causation is really just God choosing to make things happen in a regular predictable pattern.
He could, if he wanted, make the fire touch the cotton and have the cotton not burn. There's nothing in the nature of fire itself that necessitates the burning.
Now, Al Gazali's motivations were theological, not scientific. He was trying to preserve divine omnipotence to make sure that nothing in the natural world operated independently of God's will. But the philosophical move he made, the separation of observed sequence from genuine causation, that's a move that would echo down through the centuries.
Because he'd put his finger on something genuinely tricky, something that a Scottish philosopher about 700 years later would turn into one of the most famous problems in all of philosophy.
But we're getting ahead of ourselves. Let's stay with the slow unraveling for a bit. Through the late medieval period and into the Renaissance, the Arisatilian framework started to bend under the weight of new discoveries.
And the cause that took the biggest hit was that fourth one, the final cause, purpose. As thinkers began to study the natural world more carefully, to measure things, to experiment, to build devices and test predictions, the idea that nature operates according to purposes started to feel less and less useful. A rock
doesn't fall because it wants to reach the ground. A river doesn't flow downhill because it has a goal. These things happen because of forces, because of the way matter and energy interact according to rules that don't seem to care about purpose at all. The person who crystallized this shift more than anyone was probably Galileo, working in Italy in the early 1600s.
Galileo didn't spend a lot of time philosophizing about the nature of causation in the abstract. What he did was something more radical. He started measuring things. He rolled balls down inclined planes and timed them. He dropped objects and watched how they fell. And what he found was that you could describe the behavior of physical objects, with mathematical precision,