1957 Geloof en Wetenschap : Orgaan van de Christelijke vereeniging van natuur- en geneeskundigen in Nederland - pagina 31

NEED HUMAN CHOICE IMPLYPHYSICAL INDETERMINATENESS? 19 would you admit that an action of yours was not ,free'? I think we would all agree that if a prediction of our action could be written down and offered to us, and we had no power to help or hinder its fulfilment, we should admit that this particular action was not ,free' but involuntary. A sneeze, for example, at a sufficiently advanced stage is judged involuntary by this criterion. So is a simple reflex action like an eye-blink or a knee-jerk. But what of more complex acts? Suppose for example that you are about to choose between porridge and prunes for breakfast. If the state of your brain immediately beforehand indicates which you will choose, would it not be possible in principle for a super-observer to write down and offer you an infallible prediction of your choice? The short answer, if you are a normal human being, is that it would not. No matter how closely-knit the chain-mesh of cause and effect in your brain, no super-observer could deduce from it a prediction which he could offer you without fear of contradiction. The reason is simply that the state of your brain after reading his prediction would not (and could not) be the state on which he based his deductions. If he tried to allow beforehand for the effects of his prediction upon you, he would be doomed to an endless regression — logically chasing his own tail in an effort to allow for the effects of allowing for the 'effects of allowing.... indefinitely i). TWO TYPES OF HUMAN ACTION Our question has thus led us to a crucial distinction between two kinds of human actions, those which could in principle be predicted to us, and those which even in principle could not. So humble an act as the choice between porridge and prunes is separated by this test from all actions such as sneezing and blinking, which we normally term ,involuntary'. In fact, a cursory survey suggests that all actions which we term ,voluntary' are distinguished from those termed ,involuntary' by the same criterion. The remarkable fact to note is that the distinction holds good whatever the degree of physical ,determinateness' in the mechanism of the brain. The fact that no voluntary act of mine can be predicted to me is entirely compatible with the possibility that all activity is physically determinate. Whether determinate or no, the physical human ^) The basic logical point here was made first by Karl Popper (Brit. J. for Phil, of Sci. I, 191 (1950)) in a profound discussion of the limitations of predictive mechanisms.

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