Why do critical thinking and first principles complement each other?

Let's put it this way: one is responsible for "deconstructing," and the other for "building." Only by working together can they unleash their full power.

Critical thinking primarily does the "deconstructing."

It means asking "why" several times about things we usually take for granted or assume "everyone does." For example, if someone tells you a certain method is the best, you wouldn't just believe it directly. Instead, you'd ponder:

• "Is this method truly the best? Is there any evidence?"
• "Under what conditions is it best? Will it still work in a different environment?"
• "Does the person telling me this have any biases or self-interest involved?"

You see, critical thinking is like a street sweeper. It helps you clear away the unreliable "common sense," "assumptions," and "biases" that others have instilled in you or that you've formed through experience. It's responsible for challenging the status quo, helping you see clearly which parts of the ground beneath your feet are solid earth and which are quicksand.

First principles thinking primarily does the "building."

Once the ground has been cleared by critical thinking, you are left with only the most basic, core "facts" and "laws." These are first principles. It requires you not to refer to existing, pre-made things (like an existing chair), but to start thinking from the most basic materials (like wood, nails) and the most fundamental physical laws (like structural mechanics).

When Elon Musk wanted to build rockets, he didn't think, "How can I reduce the cost of existing rockets a little?" Instead, he asked:

• "What are the most basic materials needed to build a rocket?" (Aluminum alloy, titanium, copper, carbon fiber...)
• "How much do these materials cost on the market, respectively?"

He calculated and found that the material cost accounted for only 2% of the total rocket price. He then concluded that rockets are expensive mainly because of inefficient intermediate processes and entrenched production methods, not because the materials themselves are costly. This is rethinking from the most fundamental "bricks" rather than patching up an existing "house."

So, they complement each other in this way:

You first need to use critical thinking as a hammer to knock down the seemingly solid walls of "common sense," "conventions," and "authoritative opinions." Otherwise, your thoughts will be trapped inside, and you'll never have the chance to reach the foundational bricks.

Once you've knocked down the walls and cleared a space, you then use first principles thinking as a method to start from the most solid ground (basic facts), using the most fundamental bricks (core elements), to rebuild a "house" of your own—one that might have a better structure, lower cost, and higher efficiency.

Simply put: without critical thinking, you wouldn't even think of using first principles, because you'd feel that the current world is perfectly fine and there's nothing to change. But with only critical thinking and no first principles, you might become a "nitpicker" or "complainer" who can only find fault but cannot offer constructive solutions.

Therefore, one helps you clear obstacles, and the other helps you reconstruct understanding. They are a golden duo.