This is a book about how the mind works. It posits two mental states, System 1 and System 2. System 1is the state whereby we evaluate and decide instinctively, without recourse to lengthy analysis. In fact, without any analysis at all. The author uses the word ‘automatically’ here. System 2 requires a great deal of effort, taking the logic of a given situation forward step by step.

The author asserts that we use System 1 much more than system 2, partly because it gets results much more quickly, which is often necessary in life, but also because it involves less effort. We have a tendency to laziness (the author uses this word), though it might also be said that since System 1 requires less time and energy it is therefore more efficient. And this would be case were it not for the fact that System 1, though it frequently gets things right, can also get things badly wrong. We may instinctively feel or ‘know’ that something is the case when it is not. Examples are provided to illustrate this.

At first glance, the author’s theory may strike the reader as a statement of the obvious. For example, the reader may feel that System 1 is simply the unconscious at work while System 2 is the conscious. (We cannot carry out step-by-step reasoning while asleep.) But the importance of this book lies in the definition the author provides for his two systems. To take a simple example for System 1- ‘orient to the source of a sudden sound’. And for System 2 - ‘fill out a tax form’. So far so clear.

[Occasionally, examples given may be less convincing. Listed under System 1 is - ‘find a strong move in chess (if you are a chess master)’. I am not a chess master, but I used System 1 to play chess. I was a lazy player. In my opinion, a chess master is less likely to do so, since he or she will have memorised the main gambits and counter-gambits up to variation 16b at least. When playing a chess master you are not just playing the opponent but memorised chunks of Modern Chess Openings as well. Hardly instinctive.]

One of the most interesting sections of the book is where the author analyses how we react to risk, and how our reactions are guided by the situation in which we find ourselves. Again, this may seem blindingly obvious. But it is plainly an important subject since the sub-prime mortgage crisis of 2008 in the United States was made possible first, by a failure to understand and factor in risk, and secondly, by the fact that those taking risks were detached from the consequences of their own mistakes. It’s easy to take a risk if you will not suffer the consequences. (I’m not sure if this second point is in the book, but if it isn’t it should be).

If you intend to read this book there are three things to bear in mind: it is relatively long; you will need to deploy System 2 while reading it; and you will often need to ignore the thought, ‘but this is obvious’ and carry on reading.