As part of the debate about what consciousness is and how science might go about answering that question, philosopher David Chalmers proposes two kinds of problems that science must tackle to properly answer the question. The easy problems of consciousness includes the various elements of mental operations such as learning, informative processing, perception, and memory. These are not necessarily easy issues to examine but have proven more accessible to methods of modern scientific thought. As demonstrated throughout the book, scientists and researchers have begun to study and describe how some of these operations occur in the neurology of the brain and the biochemistry of the body.

The hard problem of consciousness, on the other hand, has proven intractable. Chalmers explains that hard problem as “the puzzle of why any of these mental operations are accompanied by any conscious experience whatsoever” (xv). Chalmers asks why information processing generates an inner feeling or sensation of a subjective identity rather than occurring “in the dark” (xv) free of awareness or experience. Chalmers uses this question as a way to dissect and/or reject each new theory of consciousness that researchers propose. Likewise, Pollan returns to this question throughout the book, using it as a guide for his responses to the theories he learns about and how successful he thinks they are at answering the question of what consciousness is.

The aspect of consciousness Pollan identifies is sentience, which he initially defines as “the ability of living beings to register sensations and respond intelligently” (xxxi). He complicates this definition by highlighting the way some researchers use sentience and consciousness interchangeably, and others use the term awareness in the same capacity. For the purposes of this book, Pollan specifies that sentience is the first or most elemental form of consciousness, a “kind of precursor to the full-fledged phenomenon” (13), which indicates some level of awareness, a point of view, the ability to register sensation, basic preferences, and agency, while lacking the “more evolutionarily advanced aspects” (13) like emotion, reasoning, and a sense of self.

Sentience also includes the two related terms, intelligence and cognition. Intelligence is defined as “a fixed goal with variable means of achieving it,” which suggests capability and flexibility that goes beyond mere instinct (13). Cognition, meanwhile, “involves the acquisition and processing of information about the state of one’s environment and self” (14). Neither intelligence nor cognition require consciousness but are related and generally considered to be prerequisites for consciousness.

The second aspect of consciousness Pollan explores is feeling. Feeling also goes by the terms emotion and affect. Pollan defines feelings as “the language in which the body speaks to the mind” (67-8). They are physical sensations combined with a positive or negative charge. Despite the central importance of feelings, they are not included in many theories of consciousness, such as IIT, which prioritize information processing over all else. However, some researchers, such as Antonio Damasio, believe that feeling is the foundation of consciousness, arising from the evolutionarily ancient brainstem rather than the much more recent neocortex, where information processing occurs.

Damasio and others argue that feeling is grounded in homeostasis, evolving as a useful method for the body to monitor and interpret changes to its environment and react accordingly to benefit its survival. Researchers who focus on feeling or sentience or information-processing believe that feeling is the boundary that separates living beings with consciousness and machines, which cannot (yet) access feeling authentically.

The third element Pollan identifies is thought, which is the level of consciousness associated with the neocortex. Thought differentiates human consciousness from other kinds, such as plant or animal consciousness. Pollan roughly identifies thought as the “gossamer traces of mentation” that are “preverbal, […] images, sensation, or concepts with words trailing behind” (122). William James describes thought as the “stream of consciousness” (128), a continuous flow in which thought “unfold as continuously as water, each one ‘colored’ by the preceding one and by its various contexts” (130). These colors of thought correspond with positive or negative charges, just as feelings do for Damasio, Solms, and Friston.

Researchers generally differentiate between conscious or active thought, such as the isolated concrete moments of thought that Russell Hurlburt is attempting to record and describe, and unconscious or spontaneous thought as researched by Kalina Christoff Hadjiilieva. Spontaneous thought includes “mind-wandering, daydreaming, creative thinking, mental flow, and those mysterious thoughts that come to us out of the blue” (152). Contrary to popular belief, only a small percentage of people experience thoughts in the form of inner speech or words, while many experience only visual images or vague sensations and impressions.

The fourth element of consciousness is self, which like consciousness, is difficult to define. Most humans have an intuitive understanding of the self: The self, or “I,” is the “subject of all our experiences,” which people feel to be “located somewhere within our heads” (xxxii-i). People in Western society generally believe the self is an individual, isolated identity, the “perceiver of our perceptions and the thinker of our thoughts” (xxxiii). The self seems to be comprised of subjective experience/perception and the constructing memory that constitutes an individual’s continuous existence. However, both classical philosophers and modern researchers have thus far failed to actively identify that “I” or locate the self within consciousness or the neurology of the brain.

This failure has led some to conclude that the self is not required for consciousness to exist. Science’s inability to locate the self in the brain or satisfactorily explain how perception becomes a subjective self leads directly back to the hard problem of consciousness. Meanwhile, the Buddhist tradition argues that the individual self is a fiction that isolates humans from the universal self, or state of no-self. Pollan begins to take this concept seriously in the Coda, after Western science has failed to provide an answer, thus suggesting again the limits of western thought and the biases that have made led science dismiss other modes of inquiry.

Phenomenology is a field of philosophy that studies consciousness through the exploration and description of subjective/first-person experience (or phenomena). Phenomenology crucially acknowledges that, despite the desire of Western science, consciousness cannot be studied from an objective/third-person “view from nowhere” (9) because people cannot step outside the “bubble of human consciousness” (127) they live in.

Consciousness is not only the object of study, but also the tool by which that study is conducted. Western thought has not sufficiently accounted for this discrepancy, a limitation that has hindered scientific efforts. Phenomenology attempts to deal with this limitation by examining consciousness from within the first-person subjective experience.