“Our brains are divided into two hemispheres. The left hemisphere is sequential, logical, and analytical. The right hemisphere is nonlinear, intuitive, and holistic. These distinctions have often been caricatures.” 

This is the essential divide that Pink seeks to overcome with this text. Although the differences between the two hemispheres are indisputable facts, the issue is that each hemisphere suffers beneath reductive generalizations about its functions. This essentialism has had a ripple effect; it has established a hierarchy between the two hemispheres, resulting in the prizing of those who implement left-brained traits and marginalizing of those who adhere to more right-brained attributes. 

“Running down the center is a thin vertical ridge that cleaves the brain into two seemingly equal sections […] The two halves look the same, but in form and function they are quite different […].” 

The physicality of the divide is important. Pink describes an image most people are familiar with to convey that most misconceptions about the brain’s functions come from the images we are presented; if there is a division between the hemispheres, then surely one is more important than the other. This, Pink is quick to correct, is not the case. On the other hand, the image of the two halves could suggest that they perform the same functions. This, too, is false. Rather, the book relates that these hemispheres are equal in importance even if they are unequal in function.  

“The left side, the theory went, was the crucial half, the half that made us human. The right side was subsidiary—the remnant, some argued, of an earlier stage of development. The left hemisphere was rational, analytic, and logical—everything we expect in a brain. The right hemisphere was mute, nonlinear, and instinctive—a vestige that nature had designed for a purpose that humans has outgrown.” 

For most of scientific history, the two hemispheres of the brain were universally considered separate and unequal entities. Here, Pink is articulating the scientific phenomenon that informed cultural biases.