Take the example of the woman discussed in Lishman's Organic Psychiatry. After a right-hemisphere stroke, she lost movement in her left arm but continuously denied it. When the doctor asked her to move her arm, and she observed it not moving, she claimed that it wasn't actually her arm, it was her daughter's. Why was her daughter's arm attached to her shoulder? The patient claimed her daughter had been there in the bed with her all week. Why was her wedding ring on her daughter's hand? The patient said her daughter had borrowed it. Where was the patient's arm? The patient "turned her head and searched in a bemused way over her left shoulder".(From a Lesswrong blog post about anosognosia.)
And some more, from a long comment thread to another lesswrong post (I have bolded the "money quote"):
Studies of patients with split brains have allowed us to begin to understand the functions and relative roles of different parts of our thinking organ. The left hemisphere, usually referred to as the "rational" side, is actually the rationalizing one, what neurobiologists call "the left interpreter." It is in charge of holding onto one person's current paradigm and worldview, no matter what the evidence. The left brain will distort facts if they conflict with the current held viewpoint. We like to think of ourselves as rational animals, but perhaps it would be more accurate to describe ourselves as rationalizing animals. However reasonable a view may be, it’s possible that we have acquired it for wholly irrational reasons and are now simply rationalizing it in order to maintain our self-image as consistent, rational, and moral. It’s not just a question of rationalization, either — we appear capable of making up complete falsehoods as part of this.
Massimo Pigliucci continues in the Summer 2003 issue of Free Inquiry:
In fact, the left brain can literally make up stories if the evidence is scarce or contradictory. A typical experiment was with a patient characterized by a complete severance of the corpus callosum (which connects the two hemispheres in normal individuals). He was shown a chicken leg to the right half of the visual field (which is controlled by the left brain) and was asked to pick a corresponding object. Logically enough, he picked a chicken head. The subject was then shown a house with snow to the left field (controlled by the right brain) and, also logically, chose a shovel.
The individual was then asked to explain why he picked a chicken head and a shovel. Notice that there was no communication between the two hemispheres, and that the only hemisphere that can respond verbally is the left one. Astonishingly, the left hemisphere made up a story to explain the facts while being ignorant of half of them: the shovel was necessary to clean the chicken excrement! I never cease to be amazed at the sorts of things that these experiments on cognition and brain function reveal. I’m sure that the average person would not have thought the above situation to be likely, but it clearly happened: a person made a choice for entirely sensible reasons, but because their brain was unable to understand or articulate them, it made up entirely new reasons and created a story around them.
Simply amazing — and all the more so because the belief being rationalized here was so obviously reasonable and appropriate in the first place. It’s bad enough that a person might rationalize bad beliefs, but apparently we rationalize good beliefs as well. How often do you suppose this happens? How many of our beliefs, especially the very good ones, are rationalized rather than rational?
Should be perhaps change our beliefs about qualifies as “rational”? If we did, wouldn’t that be a rationalization as well?