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People often aren't able to come up with an answer that is logical and practical when faced with making a decision. This problem happens because we approach issues with a combination of viewpoints. Experience, biases, emotion, instinct, and, of course, logic all play a role in decision-making. Thinking Fast and Slow breaks down these viewpoints into two systems of thinking – the fast and slow systems.

System 1 is a mode of thinking based on emotion and subconscious reaction. This type of thinking happens quickly, typically called "gut instinct," and can be impractical and flawed. System Two is a mode of thinking based on slow, deliberate thought and a more logical approach. By understanding how and why the two systems affect decision-making and new experiences, it's possible to learn how to make better decisions and create new ways of thinking based on reasoning.


System one: fast thinking

Biases and personal experience are the foundations of System One thinking. When faced with a decision, the first instinct is usually to approach the problem by referencing past experiences and creating associations. The tendency is to try and find solutions quickly with as little effort as possible. This "knee-jerk" reaction is very subjective and often includes elements that turn out to be irrelevant and sometimes harmful. Jumping to conclusions, false assumptions, misinformation, and a host of other pitfalls come into play with this mode of thinking. For many, this type of thinking happens uncontrollably without any conscious effort.

One of the problems with System One thinking is that this approach to decision-making means trying to make a new experience fit the existing patterns of thought. When a new experience presents itself, new types of thought should be created to fit the experience, not the other way around. For example, a doctor who has only worked independently will typically approach working in a team atmosphere by referencing past experiences and thoughts. By responding to this new experience without learning about the dynamics of groups, the chances of that doctor "fitting in" will be slim.

"A reliable way to make people believe in falsehoods is frequent repetition because familiarity is not easily distinguished from truth."

The issues with System One thinking are compounded by the fact that this type of thinking is practiced so frequently as a first resort. Even with an understanding of the problems found in this way of thinking, it's hard to slow down and take a different approach. System One thinking is easy and familiar, and even though it's often impractical or ineffective, it's a hard habit to break. While the elements that contribute to this way of thinking have their merits, without using them in a deliberately logical manner, they will continue to produce less-than-optimal results when it comes to important decisions and unfamiliar situations.

System one characteristics:

  • Creates quick impressions, emotions, and feelings
  • Occurs with little effort, often subconsciously
  • Generates a feeling of accomplishment based on quick response
  • Constructs patterns and associations for new experiences from past experiences
  • Often occurs with little examination or attention to details

"Mood evidently affects the operation of System One: when we are uncomfortable and unhappy, we lose touch with our intuition."

System two: slow thinking

Based on logic and evaluation, System Two thinking takes a practical, objective approach to making decisions and understanding new experiences. System Two thinking is infrequently used for several reasons, even though it provides better understanding and results in better decisions. This type of thinking requires conscious effort and a determined response. Better decisions and new patterns of thought are created by slowing down and taking the time to understand the unfamiliar. The ingrained habit of System One thinking is so prevalent for most people that it makes adopting the System Two approach seem difficult at best.

Slow thinking just seems to be a lot of work, and it's hard to justify the effort to slow down for the very reasons that System One is so attractive. The familiar experiences and thought patterns that are a part of System One thinking create a comfort zone that feels right. Regardless of the outcomes, the System One approach is simply too easy and automatic to give up easily. System Two thinking is often unfamiliar territory to most, so it's difficult to buy-in without understanding how this way of thinking can be more productive and effective.

"Intelligence is not only the ability to reason; it is also the ability to find relevant material in memory and to deploy attention when needed."

System Two thinking produces not only a better understanding of new experiences and better decisions, but it also creates opportunities to replace some of the irrelevant elements of System One thinking. By using System Two thinking, old thought patterns that may be based on false assumptions, misinformation, and lack of understanding begin to lose their appeal and can be replaced with objective, logical thought patterns instead. The result is a habit of thinking that becomes stronger and more consistent the more it's used. Slow, logical thinking only creates a growing ability to make better choices more frequently.

System two characteristics:

  • Requires slow, deliberate thinking
  • Creates a better understanding of new experiences and results in better decisions
  • Constructs new patterns and associations for new experiences
  • Includes reasoning, logic, and a conscious approach
  • Develops the ability to evaluate and change old thought patterns objectively

"The world makes much less sense than you think. The coherence comes mostly from the way your mind works."


Although the System Two mode of thinking is superior to the System One model in many ways, they both have value. When used together, they create a whole new way of thinking. When System 1 thinking runs into a dead end, it usually turns to System Two for resolution out of necessity. But it's the ability to use System Two thinking along with System One that creates the most benefits. When applied to the subjective elements of subconscious thinking, the logic and conscious attention of System Two helps monitor, adjust, and verify old thought patterns.

By evaluating System One thought processes using System Two thought processes, the two ways of thinking become a powerful combination. Ingrained thought patterns from past experiences are examined with a practical approach, and their validity is challenged. The result is more accurate "gut reactions" to everyday experiences and a better approach to new experiences. By slowing down and developing the skills to use these two modes of thinking together, it's possible to create an approach to experiences and decision making that uses logic and intuition effectively.