Thinking, Fast and Slow

Daniel Kahneman’s Thinking, Fast and Slow is remarkable for the strength of its perspective into human reason, the clarity of its exposition, and the (ironic) lack of self-awareness of the author’s voice. I go through these three (of many) learning points from the book in sequence below.


The book’s argument is strong and nuanced. It claims that we should be self-aware of the two perspectives that we take when we go about doing stuff. These two perspectives are analysed into three levels of description – the psychological (System 1 and System 2), the practical (Humans and Econs), and the sentimental (experiencing and remembering self). The three-level dualism can be glossed as the study of the motivational structure of the prereflective and the reflective personas.[1]

The prereflective persona is the usual mode that we assume – or, more accurately, that we find ourselves in. This is the realm of instinct, intuition and impulse that spans Kahneman’s descriptions of System 1, Humans and the experiencing self. The prereflective persona acts seemingly without thinking and is most obviously identified when we imagine doing something while being bored out of our minds or while being immersed in ‘the flow’ and becoming one with what we do. (Ideas come together at the extremes, it seems – being bored is being in a state of flow, too, in a way.[2])

Take Kahneman’s example of the veteran firefighter who had a “sixth sense of danger” and “heard himself shout, ‘Let’s get out of here!’ without realizing why.[3] At the psychological level, System 1 perceives danger out of the norm for a fire scene and instinctively activates the firefighter’s flight response. At the practical level, the Human in the firefighter determined that the risk of the operation outweighed the expected reward and decided to abandon the task. At the sentimental level, the experiencing self felt “that the fire had been unusually quiet and that his ears had been unusually hot” and flagged the incident as alarming. These modes of explanation can be thus summarised: the firefighter entered the scene and prereflectively found himself escaping from it and urging others to do the same.

The reflective persona, on the other hand, is the mode we assume deliberately – we think about ourselves and what we are doing. This is the realm of introspection, inhibition and imagination that permeates System 2, Econs and the remembering self. The reflective persona puts itself out of step with the world and takes an “outside view[4] of itself. In several ways, we see ourselves more clearly because we notice our outlines. We know what we’re thinking or feeling, we tell a story about ourselves, we judge ourselves ‘impersonally’.

Kahneman illustrates the reflective persona through the example of Orley Ashenfelter’s wine investment formula[5]. At the psychological level, System 2 abstracts from the moment to rein in and modify the instinctive judgment based on tasting the wine. At the practical level, the Econ in Ashenfelter proposed and adhered to a formula to predict wine prices to guide his investment decisions. At the sentimental level, Ashenfelter activated his remembering self[6] to select the most important variables to include in the wine investment formula. To summarise, Ashenfelter reflectively constructed a course of action to maximise his return from his wine investments.

The value of Kahneman’s argument is that it is distinguishes the prereflective and reflective personas while being clear about how they are not utterly distinct. System 1’s instincts are prone to error and must be refined through feedback from System 2. But System 2 sometimes takes System 1’s inputs for granted and may veer off-course. Econs can construct elaborate models for rational action which Humans often do not adhere to. But the assumptions of rationality for Econs must be validated by the Human experience.[7]

Interestingly, Kahneman’s preference for the reflective over the prereflective persona is reversed at the third level of description. The remembering self retains the most vivid impressions from its past experiences to make decisions, but this reflective perspective contends with the here-and-now view of the experiencing self, which Kahneman thinks is more important. But this reveals that the title of his book is a little misleading. Rather than that slow thinking reins in the excesses of fast thinking, as we are wont to think going through the first 4 sections, Kahneman’s central claim is this: if our fast thinking were optimal, we wouldn’t really need slow thinking. The instantaneous experiencing self, the motivated Human, the instinctive System 1, they are the frame of reference for Kahneman’s idea of what being human means. Slow thinking only serves to optimise (or, for the third level of description, to hinder) the proper functioning of fast thinking.[8]

The viewpoint that Kahneman puts forth in Thinking, Fast and Slow, then, is that human reason operates in the paradigm of rationality, and our slow thinking systems are mostly designed to enhance the operation of our fast thinking systems. If we agree with him and apply the lessons learnt from this principle, the book provides deep insights to help us improve.


The other strength of Thinking, Fast and Slow lies in its clarity of exposition. Kahneman takes us through decades of his illustrious research career like a master storyteller. He recalls collaborations with other respected psychologists and economists like recounting stories with old friends, and introduces the reader comfortably to his pioneering work in prospect theory and behavourial economics. He is also consistently critical, analysing others’ thought and his own with the same standard of rationality that he describes in the book.

It is to Kahneman’s credit that reading his book is like having a sublime meal: the process was enjoyable, the flavours subtle and multifarious, and on reflection it demands to be relished again. Reflexively, after getting a fast impression of the book the first time round, it is worth going through a few more times over and digesting slowly, for us to hone the intuitions we have gained.


The third learning point is to do better where Kahneman’s book falls short, which is to take its own point of view for granted. Ironically, Kahneman’s own intuition about human reason is largely a product of prereflective rather than reflective thought. He presents the view of human reason as operating in isolated, forward-looking time-slices as though it were self-evidently true. Reason just is making the right decision in the moment, in light of the present situation and future prospects.[9]

But this assumption, which he never seriously thought was worth discussing, let alone challenging, dooms his aim to effectively criticise fast thinking from the start. As he was unaware of his own preference, he could only view the fast thinking system as a flawed approximation to the ideal state needing a remedy from the slow thinking system. If put uncharitably, Kahneman was going in a giant circle and going nowhere.[10]

Against Kahneman’s assumptions, fast thinking need not be the ideal standard of human reason. Taking a page from his book (Ch. 34, Frame and Reality), his frame of reference affects his view of the two systems. Fast and slowing thinking occur along a spectrum, but Kahneman presents them as though slow thinking was helping fast thinking catch up to its own ideal state. The true dichotomy to analyse is not within this spectrum of thought but rather between the rational actor model, stripped bare of human emotions and impulses, and the view of human being as whole and complete because of its imperfections and contradictions.


The challenge for reasoning about ourselves is to respond to our reality and embrace our humanity. Thinking, Fast and Slow provides a brilliant perspective into the functioning of our reasoning side, but that is not the whole picture of our mental lives. In order to do ourselves justice, we need to take into view our emotional, aesthetic aspects too.


[1] I adapt this term from Jean-Paul Sartre’s Being and Nothingness, in which he presents his philosophy of existence. I use ‘persona’ rather than ‘self’ because the self is one of the most loaded and frustrating concepts in philosophy. (This is not to say that ‘persona’ is problem-free, only that it takes us through fewer minefields.)

[2] See David Foster Wallace’s The Pale King and Martin Heidegger’s The Fundamental Concepts of Metaphysics for a literary and philosophical take on this musing, respectively.

[3] Kahneman (2011), p. 11.

[4] Kahneman, p. 245.

[5] Ibid, p. 223.

[6] Kahneman notes that “the correlation between his [Ashenfelter’s] predictions and actual prices is above .90.” (Ibid, p. 224.) If Ashenfelter were an ideal prospective Econ and not a remembering Human, the formula should include all relevant variables and the correlation should be 1.

[7] Kahneman makes this implicit point in describing the emergence of behavioural economics to account for the weaknesses of the rational agent model. (Ibid, pp. 269-88)

[8] Kahneman occasionally praises System 1, which suggests that he holds an ideal view of its proper function and is merely focusing on obstacles to that ideal in the book. At peak function, a well-honed System 1 leads to expert intuition and ability in, say, chess. (Ibid, pp. 236-9) And he concludes by saying that System 1 “is the origin of most of what we do right – which is most of what we do.” (Ibid, p. 416)

[9] A few choice examples: “What we learn from the past is to maximise the quality of our future memories, not necessarily of our future experience. This is the tyranny of the remembering self.” (Ibid, p. 381) “Odd as it may seem, I am my remembering self, and the experiencing self, who does my living, is like a stranger to me.” (Ibid, p. 390)

[10] He does make a half-hearted acknowledgement of his narrow point of view: “We cannot hold a concept of well-being that ignores what people want. On the other hand, it is also true that a concept of well-being that ignores how people feel as they live and focuses only on how they feel when they think about their life is also untenable. We must accept the complexities of a hybrid view, in which the well-being of both selves is considered.” (Ibid, p. 402)