Changelog

• [2025-10-19 Sun] First version released.
• [2026-02-26 Thu] Add complement based on Logos' book.

Introduction

This weekend I decided to start Coursera's "Ancient Philosophy: Aristotle and His Successors" course [1], and for the first module we are introduced to Aristotle's categories.

I must confess that I found it difficult to keep myself engaged to those initial studies, since it deals with multiple abstract definitions like predicates and subjects relationships, primary and secondary substances, and more.

But things changed when our professor explained the goal of Aristotle when defining this system: answer Socrates' questions with a solid logical structured system.

After knowing this, things started getting more interesting.

Socrates' Questions

Socrates, as we know from Plato's texts, was interested in finding proper definitions and discovering essences, ex.: the universal form that makes all courageous or just actions what they are.

His method (the elenchus) revolved around:

1. Asking for universal definitions (What is X-ness itself?)
2. Testing answers for consistency and universality
3. Showing that knowledge requires understanding what something is, not just recognizing instances of it.

But Socrates never gave us a system for how to identify or classify these essences — he just kept asking questions that led others to deeper reflection.

Example questions:

• What is courage?
• What is justice?
• What is beauty?

Plato's System: the Realm of Forms

Before Aristotle, Plato already devised a system that can be used to answer those questions. However, Plato's system demands a new reality: the realm of Forms.

When Socrates asked “What is Justice?”, Plato said:

Justice itself — Justice with a capital J — is not found in the world around us, but in a higher, unchanging realm of Forms (or Ideas).

So, in Plato’s view:

• Every thing in the physical world “participates in” or “imitates” its Form.
  • Example: All beautiful things share in the Form of Beauty.
• The Forms are eternal, perfect, and immaterial.
• The particulars (individual objects) are imperfect copies of those Forms.

Aristotle's System: Bringing the Forms Down to Earth

Aristotle admired Plato but rejected the separation between the two worlds.

He argued:

“There is no world of separate Forms. The form of a thing is in the thing itself.”

So, while Plato said:

The Form of Man exists apart from all men,

Aristotle said:

The form of man exists in each man — it’s what makes him be a man.

This is the heart of their difference.

Plato	Aristotle
Forms exist separately from things.	Form and matter are inseparable within each thing.
Knowledge = grasping eternal Forms through intellect.	Knowledge = understanding the form within matter (the essence of each thing).
Metaphysics is dualistic (two realms).	Metaphysics is immanent (form and matter combined in one world).

Complement

Recently, I read the "Categories" edition from Logos [2], and it presents a more detailed explanation of this book from Aristotle, and how it connects with the órganon; i.e., the aristotelian corpus about logic.

To better understand it, we need to know the distinction between formal and material logic.

According to the scholastics, formal logic deals with the validity of the reasoning; with the question of whether the conclusion follows from the propositions. Complementing it, material logic deals with the truth of the premises and their degree of certainty.

"Categories" lives in the material logic category.

Conhecer as categorias sob as quais se distribuem os vários conceitos é útil para formular definições, e a definição é uma espécie de proposição per se nota, que pode servir de ponto de partida para uma definição.

--- [2]

For example:

Sabendo o que é "homem" e o que é "animal", entendemos que o homem é por definição um animal.

--- [2]

And this evidence can be the base for a higher reasoning.

References

• [1] - Ancient Philosophy: Aristotle and His Successors. Coursera course page.
• [2] - Editora Logos.

Disclaimer

Parts of this text were based on interacting with an AI system, although the text was edited by me.