mental models

First Principles Thinking: A Framework for Innovative Problem Solving


A first principle is a foundational proposition that cannot be reduced any further. It grounds all other assumptions that are built on top of it. Think of the theory of information, as an analogy. The bit is the most basic unit of information, while a first principle represents the basic unit of knowledge. In mathematics, first principles are referred to as axioms.
A first principle is the foundation on which further thinking can be built. Think of a tree. First principles represent the trunk and the big branches, out of which everything else springs and ramifies.

Mental models vs First principles

Mental models help us make sense of the world, by providing clear representations of how different concepts work. They don’t deal with the root/base of our thinking. Whereas first principles require us to question every assumption or model we already believe, in order to arrive at the most basic truth.

First principles thinking vs thinking by analogy

We usually rely on assumptions and heuristics when trying to understand how something works. These beliefs are backed up by repeated experience, in most cases. It’s normal and expected to lean on tried-and-tested methodologies. You can’t always play Descartes and question everything in your life.

However, when novel situations arise, we can’t rely on the same assumptions we’ve always employed in our decision-making. We need to go deeper.

When to use analogy vs first principles

So how do we decide whether we need to ditch the assumptions and reason from first principles? It depends on two factors: novelty and complexity.

Low-novelty, high-complexity. The more familiar you are with a situation, the more you can predict what will happen next, even without understanding the principles behind it. Use analogies when you’ve been in a situation many times and you can replicate the results. For example, if you know how to drive a manual transmission car, you’ll be able to get behind the wheel in any model, without feeling confused.

Low-novelty, Low-complexity. To stick to a driving example, karting fits well here. It’s pretty straightforward, you only have a wheel and 2 pedals. Even if you’ve never driven a car before, you probably are familiar with what the different parts do. In this case, both analogies and first principles can be applied.

High-novelty, low-complexity. This is the sweet spot, the territory that allows for reasoning by first principles. Let’s say you’re cooking a meal with ingredients and spices you’ve never used before. You can come up with a decent meal if you understand the order in which ingredients are added, the cooking techniques required and how to balance the flavors. Go back to the fundamental principles.

High-novelty, high-complexity These are the most unpredictable situations. Imagine rushing into the cockpit of a plane. You’re in a movie-like scenario where the pilot is dead and the only person left who can save the lives of the passengers is you, for some reason. All the first principles in the world won’t be able to help you make sense of all the buttons and levers.

first principles
Idea credit: Tomas Pueyo | Design: myself

Two frameworks

Five Whys

Every problem has as root cause and a proximal cause. The proximal cause only reveals the immediate thing that caused an event to happen. It’s only a superficial explanation. In contrast, the root cause is the underlying reason.
Five Whys is a technique elaborated by Sakichi Toyoda and was used within the Toyota Motor Corporation to get to the root of a problem.
The logic behind this exercise is to understand at a fundamental level the cause-and-effect relationship between all components of a system. By repeatedly asking “Why?,” we can bring to light the foundation of anything. Identify your problem or any statement that you can to investigate, and ask “why?.” The first answer you’ll get is probably a proximal cause. It doesn’t address the fundamental reason. Keep asking “why?” four more times, each time uncovering deeper explanations.

Socratic Questioning

Socratic questioning is a method that can be employed for many reasons, due to its versatility. It can help us get to the truth of a matter, re-frame a complex problem or simply dive deeper into our own beliefs. Most importantly, it can expose what we know for sure versus where our thinking is muddied by assumptions.

Socratic questioning usually follows this way:

  1. Understand what you actually believe. What do I believe to be the case? Where did this belief originate?
  2. Challenge your assumptions. How do I know this to be true? Why do I think I’m right?
  3. Seek evidence. What are the sources? Is there reason to doubt these sources?
  4. Entertain different perspectives. What if I’m wrong? What are some contradicting viewpoints?
  5. Explore implications. How do these findings affect my situation?

Reverse thinking

First principles thinking is applicable not just when cultivating new ideas, but also when we want to tear something down: institutions, processes or ideologies. Demolishing the old ways of doing things in light of new understanding of how the world works is a necessary component of progress and innovation. It should be encouraged.
However, we should tread this territory carefully. We shouldn’t rush to criticize something if we don’t understand why it was built or what purpose it serves in the first place. This goes back to identifying the essential foundation it was built on. Only after we have a clear idea of why something was the norm, are we justified in proposing its eradication. (This of course does not apply in all circumstances. There are flagrant moral crimes that should be abolished, no matter the reasoning that grounds them.)

Final thoughts

Learn to identify the situations when you need to stop thinking like everyone else in order to get to the core of problems by reasoning from first principles. It will make you a better thinker, a more creative person and will give you the confidence of a clear thought process. That’s priceless.


First principles thinking, Farnam Street


Model thinkers

Socratic questioning

Five whys

First principles

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