“Thus, while one may be horrified by the ravages of developmental disorder or disease, one may sometimes see them as creative too—for if they destroy particular paths, particular ways of doing things, they may force the nervous system into making other paths and ways, force on it an unexpected growth and evolution. This other side of development or disease is something I see, potentially, in almost every patient; and it is this, here, which I am especially concerned to describe.” 

Sacks is particularly interested in the ways in which neurological conditions create not only disorder or disease, but new, creative ways of being as well. Throughout the book, Sacks will search for “unexpected growth and evolution” in each and every patient he works with. This reflects Sacks’s desire to have a more holistic and nuanced understanding of how one’s neurology affects identity and perception, while also blurring the lines between health and disease.

“[…] I am sometimes moved to wonder whether it may not be necessary to redefine the very concepts of ‘health’ and ‘disease,’ to see these in terms of the ability of the organism to create a new organization and order, one that fits its special, altered disposition and needs, rather than in the terms of a rigidly defined ‘norm.’” 

Here, Sacks challenges what he and his fellow physicians view as “health” and “disease” and asks whether it is possible for someone with a neurological condition to still be viewed as healthy, whole, and valid. Each patient Sacks will work with throughout the book further tests his idea of what makes for a “normal” person or brain. By gaining a better understanding about how those with neurological conditions adapt to and thrive in the world, he opens up more opportunities to understand the many ways we can exist in our bodies. Here, for example, Sacks proposes that it isn’t so much any neurological state itself but rather the individual’s response to it that is “healthy” or “disordered.“ By this metric, Virgil is at his least “healthy” when struggling to cope with the restoration of his sight, while Jonathan’s adaptation to the loss of his color vision demonstrates his continued “health” in the wake of major injuries.