In his bestseller, Thinking Fast and Slow, psychologist Daniel Kahneman outlined the two modes of thinking that he called System 1 and System 2. Roughly speaking, System 1 mode consists of intellectual processes that are “hard-wired” into our psyche and are performed automatically, or with minimal effort. Our startled reaction to an unexpected loud noise or sexual arousal in response to a pheromone are examples of the System 1 mode, as are swinging a bat or catching a ball. System 2 consists of activities that require full attention and often sustained mental effort, such as counting the number of words in a sentence or filling out a government form. Kahneman asserts that System 1 thinking is fast and frugal, i.e., it happens almost instantaneously and demands little cognitive energy. System 2, on the other hand, is slow, but systematic, requiring full attention and consuming significant mental energy.
It is generally believed that system 1 thinking was predominant in the early development of the human brain. System 2 thinking, involving logic, abstract thought and mental modeling is believed to have evolved later with the development of the prefrontal cortex. The latest stage in the evolution of the human brain was the development of the neocortex–that part of the brain that houses our deductive power. Rational thinking, usually associated with deductive or logical analysis, is slow, methodical, tedious, and sequential. Its power lies in its capacity for abstract reasoning that enables us to generalize and reach beyond our immediate environment into realms beyond the grasp of direct observation. Deductive reasoning has empowered us to model our universe with mathematical equations, enabling us to understand and predict natural phenomena, build complex structures, construct computers, and harness nuclear energy.
However, such power comes at a cost. Deep, deductive reasoning requires great effort and concentration. It also exerts a heavy load on short-term memory and demands full attention with single-minded focus. Great mathematicians like Henri Poincaré and G. H. Hardy explained that they attempted no more than four hours a day of intense work. After that time, staying focused becomes increasingly difficult. We do not yet know why deductive reasoning is so cognitively demanding. Claude Messier, of the University of Ottawa in an interview in Scientific American, conjectured, “My general hypothesis is that the brain is a lazy bum. The brain has a hard time staying focused on just one thing for too long.” Consequently, we are reluctant to engage in prolonged deductive thinking unless it’s absolutely necessary. A less graphic description is provided by psychologist Daniel Dennett, who observed, “The rational mind is a serial virtual machine implemented–inefficiently–on the parallel hardware that evolution has provided for us.”
Joseph Heath, Professor of Philosophy at the University of Toronto amplifies this idea:
The key word here is inefficient. The mind simply didn’t evolve to support the sort of linear, explicit processing that is the hallmark of rational thought … thus the way your brain feels after writing an exam is like the way your back feels after a long day spent lifting boxes–Neither was designed for the task that it is being asked to perform.
The discipline known as “mathematics” is entirely based in System 2 thinking and some psychologists conjecture that the mental fatigue we feel when engaged for long periods in this mode of thought results from a gradual depletion of glucose in the brain. When I was a graduate student in mathematics, I asked one of my mentors, the prominent number theorist Hans Heilbronn, whether he played chess after dinner. Speaking emphatically in his German dialect he asserted, “Oh no, chess is too much like mazematics! Ven I vish to relax, I play bridge.”
