Theists like to point out that we can never prove that others (besides ourselves) have minds. The person sitting in the chair next to me may be carrying on quite a lively conversation—but how can I be sure there’s really a “mind” behind all those words. According to many theistic philosophers, I can’t. As Ronald Nash wrote in his book Faith & Reason,
No one has constructed a good argument that others have minds.
Of course, theists take it for granted that other people have minds: they see it as a basic belief, one that is quite rational and reasonable even though it may be impossible to prove. And they see this as justification for another basic belief that may be impossible to prove: the existence of a “divine mind” behind creation.
Essentially their argument is this:
No, I can’t prove that the divine mind exists, but so what? I can’t even prove that the person sitting next to me has a mind. Yet everyone agrees it is reasonable to believe in other people’s minds, therefore it must be reasonable to believe in a divine mind.
Not so fast, I say.
We learned as infants that other people have minds of their own, that their desires and intentions do not always accord with our own, and that things go better for us when we take other people’s minds (particularly our parent’s) into account. It is something every one of us learned inductively through experience and the school of hard knocks. Something which no one doubts unless they are attempting to do philosophy.
For any philosophers reading this, I’ll make it clear. The existence of other minds is an empirical observation, an inductive hypothesis which we reached as infants by essentially approaching the world the way a scientist would. Even little children can be good empiricists. Indeed, the fact that four-year olds can figure out the existence of other minds is evidence that the scientific method (albeit unconsciously) is natural to humans.
But let us become a philosopher and inductive reasoning from empirical observation is suddenly no longer good enough: we want proof. And this means, not evidence but a deductive argument from a set of premises. And here, Nash is telling us, “no one has a good argument that others have minds.” Nor is he alone. A great many professional philosophers would agree.
And yet it’s nonsense. True, no deductive argument can prove the existence of other minds. But that is because of a misunderstanding about deductive arguments. Consider:
All men have minds.
Socrates is a man.
Therefore Socrates has a mind.
That is a valid deductive argument, one which proves Socrates has a mind if its premises are correct. But premises always do one of two things: either they assert a definition (“let us say that Socrates is the name of a man”) or they assert an observed fact (“we have observed the existence of a man named Socrates”). Likewise, “All men have minds” can be taken as defining men as creatures who—by definition—have minds, or taken instead as making an empirical observation about men.
But how do we determine—ever—if an empirical observation is true? There is only one way: by inductive reasoning from observation and experience. Observational “facts” are determined inductively—not deductively. What might be termed “definitional” facts are either declared ex cathedra (a “basic belief”, in other words) or deduced by deductive argument from other definitional facts.
This is why philosophers spin their wheels trying to “prove” the existence of other minds. They are trying to reach a deductive conclusion drawn from definitional facts. Yet it is logically impossible to verify an observational fact that way. How then do we know that other minds exist? The same way the human infant learns that her parents have minds outside of her own: by inductive reasoning from experience. The same method used by scientists.
Furthermore, it follows that the conclusion of any valid deductive argument (“Therefore Socrates has a mind”) will never be an observational fact. It will always be a deduced fact. No deductive argument will ever prove that others have minds; at the same time neither will any deductive argument ever prove that the sun is fueled by nuclear fusion, or that grass is green, or any other empirically-derived observation.
This hints at what I’ve come to see as one of the major occupational hazards of doing philosophy (as opposed to, say, doing science): you come to expect important observations to be knowable by “pure reason.” And when it’s shown they can’t be known by pure reason, you lament that they are “unprovable” and therefore a matter of opinion or “faith”—or declare it a basic belief.
Again and again philosophers trip over the expectation that matters of fact are provable with a syllogism. It leads them to throw up their hands when faced with factual questions. After all a syllogism is only as good as its premises, and philosophers don’t do empirical observations. They don’t confirm premises. Philosophers evaluate arguments for logical validity—does the conclusion follow from the premises?—but philosophers are not in the business of validating premises. The philosophic method has an incredible hole: it can’t vouch for premises, it can’t determine matters of fact.
For that we need the scientific method. Or a four-year old.