Descartes' book "Discourse on the Method" was adapted into a novel.
In order to keep Descartes, who is to become the Swedish royal philosophy tutor, the servant Schluter constantly tries to talk to Descartes.
In the process, you come to understand the relationship between 'the thinking self and the truth', and finally, through methodological doubts that constantly doubt everything, you vaguely realize Descartes' philosophy of 'I think, therefore I am'.
By following Hein Schlueter's thought process of maturation, even middle school students who read the book will understand how to think rationally and logically.

"If thinking is the true nature of a person, then does that mean those who are poor thinkers or possess low standards are inhuman? There must be a difference in the character of someone like you, a good thinker, and someone like me, who lives in mediocre thoughts."
"hmm…….
yes.
They say that how deeply and accurately a person thinks shows his or her character.
“Uncivilized people who have not developed the ability to think have human forms, but it is difficult to see them as truly human.”
Schlueter was offended by these words.
This was because I thought that although I was not a savage, it was difficult to see that my level of thinking was outstanding.
He had never thought of himself as not human.
It had two eyes and two ears, a nose and a mouth, hands and feet, so it was obviously a human.
But according to Descartes, appearances were not certain.
It was difficult to determine whether it was human or not.
The ability to think, this was the only proof that one was human.
Schlueter was not confident in the evidence and therefore felt bad.
I felt like grabbing the tail.
I wanted to find fault with Descartes' words.
“What’s going on? A thoughtful person like you, Master, fell asleep because he was tired.
We don't think while we sleep.
So, are the people at that time and the people thinking about it the same or different? While sleeping, we don't think as much as savages.
No, you don't even think about it."
This time, Descartes had a stinging expression.

- From [I, the Thinker, Cannot Doubt]

“Just because you have teeth doesn’t mean you can chew food on your own.
You have to chew your food.
The same goes for reason.
You can't taste or utilize the power of reason before you use it.
There are also problems for those who use it.
If you don't use it properly, you may end up insisting that something is right when it's wrong.
“How much do you think 1+1 is?”
“That’s 2.
“If you add one apple to one apple, you get two.”
"yes.
But there are people who don't answer like that.
Some people say 11.
It's just a 1 added right next to 1.
Some people say it's 1.
If you add one drop of water to another, you still end up with one drop.
There is also a person named 3.
It's a funny story that when a man and a woman meet, they have a child.
Even if you have reason, if you use it wrongly, the answer will be different like this.
And don't fight each other, saying you're right.
The problem is more when you use your reason clumsily.
This was the problem I was struggling to solve.
The reason we misuse our reason is because we don't know how to use it well.
If you knew how, you could think like me, Schluter.
Even those who were thinking wrongly will come to know what was wrong and what is right.”
Schlueter was shocked to hear that even a servant like himself had the capacity for thought like Descartes.
I became interested in the method the owner found.

“Master! I... I also want to learn that method.
So, I want to imitate you at least as well as you, even if not as well as you.”
“You are already learning how to do it.”
“You’re learning?”
"huh.
You'll realize it later."
- From [Realizing How to Think]

“First of all,
The point is, don't accept anything as fact unless you are absolutely certain of it.
Always keep this attitude when solving problems, but you need to have a plan.
The second method is to break the problem down into as many pieces as possible.
If the problem is too big, it's difficult to deal with.
“It’s the same principle as cutting pizza into appropriately sized pieces to make it easier to eat.”
“I know that method very well.
That's the first thing I do when doing housework.
If you divide the work that needs to be done into items and then assign a person in charge, it will be very easy to do.
“What about the third one?”
“Third, think about the order.
There is a principle here.
It starts with easy and simple things and progresses step by step to difficult and complex things.
We need to start with something that is easy and simple and that everyone recognizes.
Then, the last thing to do is to go through the order and check that you haven't missed anything.
“That’s all there is to it.”
- From [Proving the Existence of God]

--- From the text