The expert suggested that apparatus could be passed on from one investigator to another:  the professor replied that few men can use apparatus designed for some one else’s purpose, and that the cost of reconstruction would exceed the cost of new machines.  In short, he completely riddled the argument from analogy set up by the expert.[27]

A notable example of conclusive refutation of an argument based on a false analogy is to be found in William James’s Ingersoll Lecture on Immortality.  He took up the ordinary argument against the immortality of the soul, which, starting from the accepted physiological and psychological formula, “Thought is a function of the brain,” reasons that therefore when the brain dies and decays, thought and consciousness die, too.

This, then, is the objection to immortality; and the next thing in order for me is to try to make plain to you why I believe that it has in strict logic no deterrent power.  I must show you that the fatal consequence is not coercive, as is commonly imagined; and that, even though our soul’s life (as here below it is revealed to us) may be in literal strictness the function of a brain that perishes, yet it is not at all impossible, but on the contrary quite possible, that the life may still continue when the brain itself is dead.

The supposed impossibility of its continuing comes from too superficial a look at the admitted fact of functional dependence.  The moment we inquire more closely into the notion of functional dependence, and ask ourselves, for example, how many kinds of functional dependence there may be, we immediately perceive that there is one kind at least that does not exclude a life hereafter at all.  The fatal conclusion of the physiologist flows from his assuming offhand another kind of functional dependence, and treating it as the only imaginable kind.

When the physiologist who thinks that his science cuts off all hope of immortality pronounces the phrase, “Thought is a function of the brain,” he thinks of the matter just as he thinks when he says, “Steam is a function of the teakettle,” “Light is a function of the electric circuit,” “Power is a function of the moving waterfall.”  In these latter cases the several material objects have the function of inwardly creating or engendering their effects, and their function must be called productive function.  Just so, he thinks, it must be with the brain.  Engendering consciousness in its interior, much as it engenders cholesterin and creatin and carbonic acid, its relation to our soul’s life must also be called productive function.  Of course, if such production be the function, then when the organ perishes, since the production can no longer continue, the soul must surely die.  Such a conclusion as this is indeed inevitable from that particular conception of the facts.

Rut in the world of physical nature productive function of this sort is not the only kind of function with which we are familiar.  We have also releasing or permissive function; and we have transmissive function.