Recent studies have confirmed James' assertion. Robert Burton, MD is a board-Certified Neurologist and Psychiatrist. He has recently written a book entitled: On Being Certain: Believing You Are Right Even When You're Not.
He gave an interview in Scientific American about the book. In the article he says: There are two separate aspects of a thought, namely the actual thought, and an independent involuntary assessment of the accuracy of that thought .
This is illustrated by the Muller-Lyer optical illusion:
Even when we consciously know and can accurately determine that these two horizontal lines are the same length, we experience the simultaneous disquieting sensation that this thought—the lines are of equal length—is not correct. This isn't a feeling that we can easily overcome through logic and reason; it simply happens to us.
This sensation is a manifestation of a separate category of mental activity—-unconscious calculations as to the accuracy of any given thought. On the positive side, such feelings can vary from a modest sense of being right, such as understanding that Christmas falls on December 25, to a profound a-ha, "Eureka" or sense of a spiritual epiphany. William James referred to the latter—the mystical experience—as "felt knowledge," a mental sensation that isn't a thought, but feels like a thought.
Once we realize that the brain has very powerful inbuilt involuntary mechanisms for assessing unconscious cognitive activity, it is easy to see how it can send into consciousness a message that we know something that we can't presently recall—the modest tip-of-the-tongue feeling. At the other end of the spectrum would be the profound "feeling of knowing" that accompanies unconsciously held beliefs—a major component of the unshakeable attachment to fundamentalist beliefs—both religious and otherwise—such as belief in UFOs or false memories.
Why do people like to be certain? Burton says that just as certain drugs, sex, gambling, and so on, provide a reward to the brain which causes it to want to repeat the action, even so, certainty provides reward. He says:
It is quite likely that the same reward system provides the positive feedback necessary for us to learn and to continue wanting to learn. The pleasure of a thought is what propels us forward; imagine trying to write a novel or engage in a long-term scientific experiment without getting such rewards. Fortunately, the brain has provided us with a wide variety of subjective feelings of reward ranging from hunches, gut feelings, intuitions, suspicions that we are on the right track to a profound sense of certainty and utter conviction. And yes, these feelings are qualitatively as powerful as those involved in sex and gambling. One need only look at the self-satisfied smugness of a "know it all" to suspect that the feeling of certainty can approach the power of addiction.
All human beings seem to feel better if they have certainty about something. The feeling of uncertainty is not pleasant. We seek an explanation. Some psyches seem to have more difficulty dealing with uncertainty than others even leading to a strong sense of frustration or despair. I tend to think that many religious fundamentalists tend to fall within in this category but so would those that are sometimes called fundamentalist atheists . So would some political commentators (especially on Fox and MSNBC) fall within this classification. It will be fascinating to see what further research on this matter discovers. I agree with Burton's conclusion: Only in the absence of certainty can we have open-mindedness, mental flexibility and willingness to contemplate alternative ideas . When one is dogmatically certain he has arrived at the truth, learning has ceased.
Below is a lecture that Burton gave related to his book: