The free energy principle: it’s not about what it takes, it’s about what took you there


Philosophical writings on the free energy principle in the life sciences often give the impression that minimising free energy is sufficient for life. But minimising free energy is not a sufficient condition for life. In fact, one can perfectly well conceive of a system that actively minimises its free energy, and for this very reason moves inexorably towards death. So, where does the assumption of this entailment relation come from? There is indeed an entailment relation, but it goes the other way around: life entails minimising free energy. Put another way, if you exist, now, under the right conditions, it is because you’ve done something like minimising your free energy. However, the question of whether you will exist tomorrow cannot be settled purely by resorting to the fact that you will minimise your free energy to get there. The simple point I make in this paper is that the free energy principle is not concerned with the sufficient conditions of existence, but rather with what must have been the case, given that you exist. It’s not about figuring out what it takes to be alive; it’s about figuring out what took you there.

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Fig. 1


  1. 1.

    It is important to note that the FEP includes processes other than free energy minimisation. It also includes expected free energy minimisation (and generalised free energy minimisation, (Parr and Friston 2019)). While minimising free energy endows the organism with postdictive inference, minimising expected free energy endows the organism with predictive inference. This is due to the simple reason that the outcomes and states involved in the inference process under expected free energy minimisation are in the future, not the present. Effectively, this means that inferring one’s beliefs about states of the world means inferring what will most likely be seen under those beliefs, and under a given sequence of action to be engaged (i.e., action policy).


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I want to thank Paul Badcock, Paul Griffiths, Mark Colyvan, Christopher Whyte, Pierrick Bourrat, Joshua Christie, Christopher Lean, Peter Takacs, Carl Brusse, Stefan Gawronski, and Walter Veit for helpful comments on earlier versions of this paper.


Work on this article was supported by the Australian Laureate Fellowship project A Philosophy of Medicine for the 21st Century (Ref: FL170100160) and by a Social Sciences and Humanities Research Council doctoral fellowship (Ref: 752–2019-0065).

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Correspondence to Axel Constant.

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Constant, A. The free energy principle: it’s not about what it takes, it’s about what took you there. Biol Philos 36, 10 (2021).

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  • Free Energy Principle
  • Postdiction
  • Prediction
  • Historical sciences