Nobody has trouble with this form of logic; we understand the abstract form and realize that it generalizes freely:
All glorks are frum.
Therefore, Skeezer is frum.
Presto — a new way for forming beliefs: take what you know (the minor and major premises), insert them into the inferential schema (all X’s are Y, Q is an X, therefore Q is a Y), and deduce new beliefs. The beauty of the scheme is the way in which true premises are guaranteed, by the rules of logic, to lead to true conclusions.
The good news is that humans can do this sort of thing at all; the bad news is that, without a lot of training, we don’t do it particularly well. If the capacity to reason logically is the product of natural selection, it is also a very recent adaptation with some serious bugs yet to be worked out.
Consider, for example, this syllogism, which has a slight but important difference from the previous one:
All living things need water.
Therefore, roses are living things.
Is this a valid argument? Focus on the logic, not the
The poor logic of the argument becomes clearer if I simply change the words in question:
Premise 1: All insects need oxygen.
Conclusion: Therefore, mice are insects.
A creature truly noble in reason ought to see, instantaneously, that the rose and mouse arguments follow exactly the same formal structure (all X’s need Y, Z’s need Y, therefore Z’s are X’s) and ought to instantly reject all such reasoning as fallacious. But most of us need to see the two syllogisms side by side in order to get it. All too often we suspend a careful analysis of what is
What’s going on here? In a system that was superlatively well engineered, belief and the process of drawing inferences (which soon become new beliefs) would be separate, with an iron wall between them; we would be able to distinguish what we had direct evidence for from what we had merely inferred. Instead, in the development of the human mind, evolution took a different path. Long before human beings began to engage in completely explicit, formal forms of logic (like syllogisms), creatures from fish to giraffes were probably making informal inferences, automatically, without a great deal of reflection; if apples are good to eat, pears probably are too. A monkey or a gorilla might make that inference without ever realizing that there
The capacity to codify the laws of logic — to recognize that
Studies of the brain bear this out: people evaluate syllogisms using two different neural circuits, one more closely associated with logic and spatial reasoning (bilateral parietal), the other more closely associated with prior belief (frontal-temporal). The former (logical and spatial) is effortful, the latter invoked automatically; getting the logic right is difficult.
In fact, truly explicit reasoning via logic probably isn’t something that
Once we decide something is true (for whatever reason), we often make up new reasons for believing it. Consider, for example, a study that I ran some years ago. Half my subjects read a report of a study that showed that good firefighting was correlated with high scores on a measure of risk-taking ability; the other half of the subjects read the opposite: they were told of a study that showed that good firefighting was
Then, as social psychologists so often do, I pulled the rug out from under my subjects: “Headline, this news just in — the study you read about in the first part of the experiment was a fraud. The scientists who allegedly studied firefighting actually made their data up! What I’d like to know is what you really think — is firefighting really correlated with risk taking?”
Even after I told people that the original study was complete rubbish, people in the subgroups who got a chance to reflect (and create their own explanations) continued to believe whatever they had initially read. In short, if you give someone half a chance to make up their own reasons to believe something, they’ll take you up on the opportunity and start to believe it — even if their original evidence is thoroughly discredited. Rational man, if he (or she) existed, would only believe what is true, invariably moving from true premises to true conclusions. Irrational man, kluged product of evolution that he (or she) is, frequently moves in the opposite direction, starting with a conclusion and seeking reasons to believe it.
Belief, I would suggest, is stitched together out of three fundamental components: a capacity for memory (beliefs would be of no value if they came and went without any long-term hold on the mind), a capacity for inference (deriving new facts from old, as just discussed), and a capacity for, of all things,
Superficially, one might think of perception and belief as separate. Perception is what we see and hear, taste, smell, or feel, while belief is what we know or think we know. But in terms of evolutionary history, the two are not as different as they initially appear. The surest path to belief is to see something. When my wife’s golden retriever, Ari, wags his tail, I believe him to be happy; mail falls through the slot, and I believe the mail has arrived. Or, as Chico Marx put it, “Who are you gonna believe, me or your own eyes?”