It appears to be quite difficult to define agency in a metaphysical sense in a deterministic world. All handling I have seen suggests agents "choose" between paths, and thus require the system to be non-deterministic.

Are there any philosophical approaches which support the reduction of a non-deterministic system into a deterministic one in a non-randomly selected way without invoking the concept of agency?

  • I could imagine this happening in some “strong” forms of mind-body dualism, where the actions of the body are totally deterministic, but the mind is a non-deterministic pure observer which believes incorrectly that it’s a free-willed agent in control of the body. Commented Jan 24, 2021 at 18:11
  • What is "reduction of a non-deterministic system into a deterministic one in a non-randomly selected way"? If a system "reduces" to a deterministic one then it is just deterministic. Do you mean explaining how the "illusion" of free will and agency arises in sufficiently complex deterministic systems, as compatibilists describe? Or something like MWI, where evolution in each branch appears indeterministic although the totality of branches evolves deterministically?
    – Conifold
    Commented Jan 25, 2021 at 4:52
  • @Conifold There may be some imprecision in how I'm wording it because I'm still exploring the theory. The lines drawn around "the system" are probably inconsistent. As a specific case, I'm thinking of a unstable equilibria (like a ball at the top of a smooth hill) which, on its own, can result in the ball rolling in any direction. However, due to a choice made by a metaphysical entity in a larger system that includes non-physical entities, the ball can only roll in one direction. I think it would be sufficient to say that the sub-system consisting of physical things is reduced...
    – Cort Ammon
    Commented Jan 25, 2021 at 15:52
  • ... to a deterministic thing up to the boundary conditions of the physical system. However, that's getting into a more specific wording, it's probably a wrong wording, and its too precise to get answers like armand's.
    – Cort Ammon
    Commented Jan 25, 2021 at 15:53
  • This sounds similar to Boussinesq's Reconciliation of Mechanical Determinism with Moral Freedom, see History of the study of indeterminism in classical mechanics. He exploited the non-uniqueness of solutions to non-Lipschitz DE instead of boundary conditions, which is resolved by a non-physical "guiding principle".
    – Conifold
    Commented Jan 25, 2021 at 18:44

3 Answers 3


In Spinoza's Ethics the world is seen as fully deterministic and agency is a matter of perspective:

People think they make choice and act on the world (i.e. they see themselves as having agency), but in the grand scheme of things (from Nature's perspective) they just put in actuality what previous events set them to do anyway. It is to say, we think we change Nature, but we are just the way ("modes") by which Nature realizes itself. The reason we see ourselves as agent is that, most of the time, we ignore (we dont even perceive) what determined us to act the way we did.

The thing is (and this is commentary, not in the book), we all perceive ourselves and people around us as having this agency and act according to this perception, so although illusory the concept of agency is still relevant. Think of it like the value of a ten dollar bill, which is $10 only as long as everybody thinks it is $10.

So, people have agency from their point of view, but it is an illusion that does not count in the absolute, is how Spinoza reconcile determinism with agency.


All handling I have seen suggests agents "choose" between paths, and thus require the system to be non-deterministic.

I don't believe that choice (or agency) requires non-determinism. Even if it is predetermined that I will choose A rather than B, the fact remains that at some point I do choose A rather than B. A pre-determined choice is still a choice. It is, however, a choice with the quality that one is pre-determined to make it.

Some may argue that a pre-determined choice is NOT a choice at all. That seems to me to be a choice about how language ought to be used, and I don't find it compelling.


There is no concept of agency in a deterministic world.

Agency is the capability to initiate actions. Determinism does not include any such capability.

A non-deterministic system can be reduced to a deterministic system only by removing all things not possible in determinism. I have no idea how that could be done.

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