Human Rationality

Human Rationality

By on Oct 17, 2016

We like to think of ourselves as “rational” human beings. But psychological research has shown that the assumption of rationality as defined by the Enlightenment is false. Our brains don’t make decisions based on probability and statistics.1 Instead, our brains decide based upon information within our conscious awareness AND information outside of that awareness.

Feelings, for instance, which are not always within our conscious awareness drive our decision-making. Neuroscientist Antonio Damasio provides one of my favorite examples of decision-making without feelings, or what Damasio calls somatic markers. He once had a patient with ventromedial prefontral brain damage who had his intellect in tact but had diminished emotional responsivity. One day, Damasio watched as the patient attempted to make his next appointment. He stood there for nearly half an hour as the patient walked him through “a tiresome cost-benefit analysis, an endless outlining and fruitless comparison of options and possible consequences” (p. 193).2 It was all Damasio could do to “listen to all of this without pounding on the table and telling him to stop.”

So while the patient could reason using probability and statistics, he had no sense of feeling to inform his reasoning, thus, impairing his ability to make even a small decision.

Spock isn’t looking so smart now, is he?   

Biases outside of conscious awareness also inform our decisions. And what can seem disturbing about these implicit biases is that they can contradict how we view ourselves. That’s because implicit biases are based on past experiences – whatever your brain has been exposed to.3 So even if you consider yourself someone without racial biases, because your brain has been exposed to all sorts of cultural racist stereotypes (some subtle, some not so subtle), you will likely have an implicit bias about someone from another race or even your own race! This doesn’t make you a “bad” person. It just makes you human. (Of course, not all implicit biases are negative; there are positive ones, too.)

Discarding the classical myth of rationality is important for all of us, and it's something we should talk to our children about. Understanding how our brains actually reason enables us to self-reflect more deeply, grow, and make better decisions. As psychologist Mahzarin Banaji states in the audio story below:

Finding out that we’re biased need not mean that we have to remain biased.

And since every single one of us has implicit biases, wouldn't it be great if we could support each other's growth by lovingly holding the mirror up to one another so we might see our implicit biases in our own behaviors instead of shaming one another for having them? We could evolve together!


  1. Gigerenzer, G., & Goldstein, D. G. (1996). Reasoning the fast and frugal way: Models of bounded rationality. Psychological Review, 103(4), 650-669. doi: 10.1037/0033-295X.103.4.650
  2. Damasio, A. R. (1994). Descartes' error: Emotion, reason, and the human brain. New York, NY: Penguin Books.
  3. Greenwald, A. G., & Banaji, M. R. (1995). Implicit social cognition: Attitudes, self-esteem, and stereotypes. Psychological Review, 102(1), 4.


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