What Do Frogs And Steam Trains Have To Do With The Human Mind? Huxley’s Epiphenomenalism And Mental Causation

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Difficulty: A-Level/Undergraduate/Masters


  1. Contents
  2. Introduction
  3. The (Immoral) Science Experiments Of The Victorians
  4. Enter Huxley
  5. Huxley’s Opponent: Mental Causation
  6. Rejecting Common Sense: Enter Epiphenomenalism
  7. Cars, Steam Trains And Epiphenomenalism
  8. No Fans For Epiphenomenalism
  9. References/ Further Reading


The 19th century was an exciting time to be alive. Incredible inventions were being discovered (such as the steam engine) new scientific theories were being developed (such as Darwin’s theory of evolution) and new philosophical positions were being created (such as utilitarianism). The Victorians were also fascinated with carrying out lobotomies and decapitations on innocent frogs. So it was a terrifying time if you were a frog. Or any other animal to be fair. However, while deeply unethical, such experiments led to a new philosophy around how the body and mind interacted. It is not talked about much as a valid philosophical position today, other than as a warning for other positions. That position is epiphenomenalism.

The (Immoral) Science Experiments Of The Victorians

During the 19th century, many scientists became obsessed with carrying out decapitations on frogs and other similar, torturous experiments (always have to love the Victorians for their commitment to animal welfare). However, some interesting observations arose from these experiments. For instance, it was discovered that frogs could swim despite parts of their brains being destroyed.

Comparisons were also drawn to medical cases with humans. For instance, in 1870, a French soldier was observed by Thomas Huxley being able to carry out complex tasks such as reloading a gun despite the soldier having severe brain damage. Some individuals, such as Huxley, argued that neither the frogs nor the soldier were conscious due to the destruction of parts of their brain. However, despite this, both the frogs and soldier were still able to carry out complex tasks. If correct, Huxley believed that this had significant philosophical implications.

Enter Huxley

Huxley was born in 1825 and was a natural scientist. In his younger years, he joined the royal navy and travelled the world studying various different species of animal (again, thoroughly appreciating animal rights). He then went on to be a lecturer in London and was on multiple boards for education. Controversially for the time, he was an ardent defender of Darwin’s theory of evolution, controversial because it was a significant challenge to the church who was the main body of authority at the time.

In 1874, Huxley gave an address to the British Association For The Development of Science named ‘On the Hypothesis that Animals are Automata; and it’s History.’ In it, he defended his idea of how the mind and body interacted (mind-body theory) as a result of his experiments.

Huxley’s Opponent: Mental Causation

Before we look at Huxley’s position, we must first look at the point he was arguing against. This position is mental causation. This is the idea that the mental has causal power. Most people believe in mental causation. Even those who do not study philosophy believe in this, even if it is subconsciously. Most people would argue that, if we turn on a kettle, this is because we have a mental state that wants us to turn on the kettle. This may be because we want to make a cup of tea or fill up a water bottle. If we didn’t have these mental states then we wouldn’t turn on the kettle.

Rejecting Common Sense: Enter Epiphenomenalism

However, despite the evident nature of mental causation, Huxley challenged the idea of mental causation. To Huxley, the soldier and the decapitated frog showed that individuals could carry out actions even when they weren’t conscious. He argued that this showed that, even when there are no mental states, physical actions would occur. Thus, he challenged whether the mental had any causal power at all. He believed instead, that the physical alone was capable of carrying out actions. The mental had no causal power. This position became known as epiphenomenalism.

Cars, Steam Trains And Epiphenomenalism

This position may appear odd to most. However, it can be understood by imagining the shadow of a moving car. The physical mechanics carry out all of the actions. Nothing else is needed for the movement of the car other than the physical mechanics. However, from the car’s motion, a shadow is cast. This shadow plays no role in the action of the car. It is merely produced by the physical action. Another comparison Huxley used was to the whistle of a steam train. Again, the action of the steam train is physically complete without the whistle. The train would move whether there was a whistle or not. It is produced but has no causal bearing on the movement of the train.

In the same way, Huxley viewed the mental as the shadow of the brain. When turning on the kettle on, the physical action occurs. In some very botched science terms, neurons fire in your brain which cause your arm to move. and turn on the kettle This process produces the biproduct of wanting tea. However, this want for tea has no causal power. The physical mechanism is enough to carry out the action without the mental. The mental is merely a product of the physical process.

No Fans For Epiphenomenalism

It is safe to say not many philosopher’s have promoted Huxley’s view. While explaining mental causation is a huge problem in the philosophy of mind (more on that in a later blog) not many would want to argue that the mental is a ‘dangler’. It is clear that what we perceive as the mental does have some kind of effect. It is obvious to everyone. Philosopher’s don’t want to deny that, when we want to boil a kettle, what causes us to boil the kettle is the fact our mental states chose to. It would be too counterintuitive to deny this. Further, it has significant impact on our free-will. No mental causation would mean no personal responsibility. This is not a conclusion philosophers often willingly concede. Because of this, it has been argued that there are more promising ways to solve this problem such as reductive or non-reductive physicalism.

References/ Further Reading


Jaegwon Kim, Philosophy of Mind, 2010, Chapter 7 ‘Mental Causation’ Available here (affiliate link)








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