For Descartes, reality consists of two fundamental substances: the mental, and the physical.

The mental substance is distinct from the physical substance in that it is not bound by the deterministic, natural laws. This, in turn, implies free-will.

However, if the mind is to control the body, and if the body is, in fact, governed by the laws of a deterministic universe, isn't, then, the mind incapable of free-will?

By definition, the notion of free-will is the denial that determinism applies to the actions of human beings. Even if we suppose that the mind is not subject to determinism, if the body is then is the mind not also restricted by the natural laws?

  • At the time of Descartes it was not believed that physical laws are deterministic, and there was, therefore, room for mental on physical causation to fully decide the outcomes. The notion of "free-will" is fuzzy, and on many positions it is not the denial that determinism applies to physical actions. Stoics held even before Descartes that while actions are predetermined mind remains, in part, independent of them and one can freely choose "attitudes". See also compatibilism, where free will is defined so as to be consistent with determinism.
    – Conifold
    Oct 9, 2021 at 0:03
  • For a thorough critique of this inconsistency from Descartes, see Spinoza's Ethics.
    – armand
    Oct 9, 2021 at 0:53

1 Answer 1


First, the Universe is not deterministic. The laws of classical physics are, but the reality they describe is not.

The mind is a living brain's capacity to process information. It is questionable whether we can call information a substance in its own right. As information is always represented as configurations of physical matter or energy, it might be more correct to say that information is an emergent property of the physical.

Nevertheless, information processing is not governed by laws of physics. Thoughts, opinions, preferences, emotions, memories, future plans, imagination, decisions, etc. have no measurable physical properties, there are no parameters to put in an equation for calculation. Mental events cannot be caused by physical events.

Free will is the ability to make decisions and implement them as physical actions. It is debatable whether the decision to act actually causes the physical muscle action. We may have to introduce the concept of control. The brain's physical activity provides the energy needed to send the neural signals to the muscles. But the decision controls which muscles receive the signals.

  • "Mental events cannot be caused by physical events." citation needed. I can't help but notice that drunk people don't react to stimuli like sober people do. So the physical event of drinking alcohol must necessarily be somewhat cause of the mental event that drives their reaction (and that's supposing there actually is such a thing as a purely mental event).
    – armand
    Oct 13, 2021 at 8:10
  • Reactions to stimuli are not mental events. They are called spinal reflexes. Oct 13, 2021 at 10:20
  • Nice dodge. But getting insulted is a stimulus too. And if I insult a drunken man there is a higher probability that he punches me back than if he was sober. That he takes the decision to punch me back. Because he is physically drunk. Note that otherwise I have to agree with your point: neural reactions is all there is to the decisions we make.
    – armand
    Oct 13, 2021 at 11:37
  • You may increase the probability of a violent response, but you cannot cause any mental event. There is no causal connection between your insulting action and the drunken man's punching action. Neither can the physical drunkenness cause any actions. He may be less capable of making wise decisions, but they are still his decisions causing (or controlling) his actions. Oct 14, 2021 at 8:20
  • What is this nonsense? You can't both admit that the alcohol influences his decision and pretend that there is no causal link. It's one or the other.
    – armand
    Oct 14, 2021 at 8:59

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