Socrates
Plato
Aristotle
Sophism
Skepticism
Stoicism

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“The only socially safe lifestyle is to be neither remarkably good nor remarkably bad.”

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Socrates (469-299 BC)

Probably the second most influential and important human being who ever lived.
Never wrote a book.
The foundation of most of Western philosophy (and science) is Aristotle, Aristotle is 75% Plato, and without Socrates, no Plato.
Socrates is to philosophy what Jesus is to religion. Like Jesus, Socrates divides mankind. He died a martyr for his beliefs after an unjust trial. The only great philosopher executed by his society.
Many love him (Calvin, Shelley, John Stuart Mill, Heidegger, Kierkegaard, Maritian), just as many are his enemies (Spinoza, Luther, Rousseau, Schiller, B. Rusell, Nazi philosophers, Communists, G. Sorel, Jeremy Bentham, Mathew Arnold, Nietzsche).
He was offensive to Athens, the world’s most enlightened, tolerant, and democratic society in history (just as Jesus was offensive to the world’s most religious society).
What was the offense? His method and his teaching.
His method: Consists of cross-examining ideas. Lesson one (on ignorance): We do not know what we think we know; there are only two kinds of people: the fools, who think they are wise, and the wise, who think they are fools (he inevitably showed the inept defenders of foolish ideas as fools).
His teaching: Your identity is in your soul, not your possessions or your body, and that the care for the soul by wisdom and virtue was the only really necessary thing, and only fools reject it:

The task of philosophy, and of life, is to “know thyself.”
To know the human self, you must know its telos, its purpose, its end, its summon bonum or “greatest good”.
This greatest good is not wealth, pleasure, power, fame or honor but virtue, which is not just good deeds but good character.
This key to the good life resides in the soul. For “the true self is the soul.”
The soul is so alive that it is impervious to death: “the soul is immortal.”
“No evil can happen to a good man in this world or the next” - Good and evil do not happen, they are chosen.
“The cause of evil is ignorance” — that is, not knowing yourself, identifying the self with the body and its needs rather than with the soul.
“Virtue can be taught” - but not by lectures. It is taught by God alone or, by men, by Socratic method.
It can be taught because knowledge of true values is innate in us.
Philosophy seeks the truth about these values by defining terms like “Justice,” “Soul”, “Virtue,” “Death,” “Piety,”, “Courage,” “Friendship,” “Love,” etc. to get at the essences, the essential natures of such things.

Socrates and Sophists together revolutionized the content of philosophy as well as the method, they were the first to turn the attention of philosophy to the questions about the nature of man, human life and moral values: the questions of human existence. In this sense he was the first existentialist.

Plato (427-347 BC)

Plato’s books are to Philosophy what the bible is to religion. He wrote the earliest complete books of philosophy that we have, and their appeal today is as great as it was 2400 years ago.
He wrote thirty (some say thirty six) dialogues and founded the world’s first university, the Academy, which lasted 900 years and was free and open to all, including women. It´s curriculum integrated the teaching of arithmetic, geometry, astronomy and music ( “quadrivium”) and of grammar, rhetoric & logic ( “trivium”).
He saw the essence of Philosophy as a dialogue with the soul, with other people and with the sought-for truth above the self. His most famous dialogue is The Apology, or defense of Socrates. His dialogues always end with some truth that is timeless.
His philosophical interests spanned individual morality and politics (covered in the Republic and The Laws dialogues).
The heart and soul of Platonism (and the most notorious theory in the history of philosophy) is his Theory of Forms, known as Theory of Ideas due to a misleading translation of the word idea to the English language. The key distinction is that ideas exist only in our minds while Plato’s forms exist outside minds, and they are objective. Our ideas can be false; they can be mere opinions as they are judged by whether they conform to their objects. Just as the idea that the colleague I met through Zoom is 1.6 feet tall is proved false when I meet him in person. Or the false idea that any interior angle of a triangle can have more than 180 degrees, which is judged based on the standard for real triangularity. Our ideas, opinions and beliefs change, just as our minds can change. But triangularity cannot change, nor the height of my colleague. These are forms, natures, essences, what’s.
He offers three arguments for the existence of forms:
- The metaphysical says that the true Being is unchangeable. Since both the material world known by the senses and the world of our thoughts and opinions are changing, then, true Being cannot lie neither in the matter nor in the mind but in the form.
- The epistemological says true knowledge is of unchanging universal truths (like 2+2 =4). So, the source of true knowledge cannot be (again) the changing things in the material world known by the senses nor in the world of our thoughts and opinions. If knowledge is possible, there must be a non-sensory reality.
- The moral argument says that the world of Forms is necessary to account for ideals. We strive for as-yet-unrealized goals like beauty, happiness, justice, and eternal love which do not exist in the material world (that’s why we strive for them) nor perfectly in our minds or will. But if they existed nowhere, they could not motivate our striving and acting. This is why they must exist beyond both our minds and our world and they must be real because they cause our minds and our world to change in their direction.
The “parable of the cave” describes these arguments by implying that the prisoners in the cave can only see their immediate world of material things and thoughts and assume it is all that exists, only the prisoner that leaves the cave learns that there is a further reality that is worth knowing. It implies metaphysical conversion from ordinary “cave” thinking to “Platonic” thinking; from thinking that our ideas are images of things to thinking that things are images of the ideas. Thus, the standards is neither our minds nor the visible world but the Forms.
He was the first to clearly map the soul’s three essential powers or faculties: the mind, reason or intellect; the will (or “spirited part”) and the emotions (or “appetites”). These are the basis for his “four cardinal virtues”: (1) prudence or wisdom, (2) fortitude or courage, (3) moderation or self-control, and (4) justice.
His successors at the Platonic Academy eventually came to doubt the existence of the Platonic Forms. This left no knowledge at all in the sensory world which changed when Aristotle introduced the immanency of Forms). This motivated the reign of skepticism in the Academy, and “academic” became a synonym for “skeptic”.
His thinking can be summarized as follows: Metaphysics -> ideas & things; Anthropology-> soul & body; Epistemology-> reason vs sensation; Ethics -> wisdom.
Just as there has never been another Socrates there has never been another Plato. Socrates was poor and ugly, Plato was rich and handsome (probably a wrestler), and his given name was Aristocles.

Aristotle (384-322 BC)

He studied at Plato’s Academy and stayed there for twenty years as Plato’s greatest student.
He eventually founded his own university (the Lyceum) and his own philosophical system.
He was called the “peripatetic” (walker-around) because he would lecture while his pupils walked (for him walking was good for philosophizing - stimulating the conscious reason) and lying down for poetry (stimulating the imagination or unconscious, Freud would agree with this).
He thought the earth was the center of the universe but he taught that it was not flat but a sphere, as did many others after him, especially in the Middle Ages. Thinking that all premoderns believed otherwise is a modern superstition.
Many of Aristotle’s books perished when the library of Alexandria was destroyed. Some of his manuscripts were found in 80 B.C. by Roman Soldiers. They were copied in Rome, then brought to Syria after the fall of Greece and Rome, then to Iraq and Iran, where they were translated from Greek to Latin to Syriac and to Arabic. The books recognized as his today are compilations and anthologies edited by Andronicus of Rhodes.
There are 2000 pages of text from Aristotle (and about 1000 from Plato).
He classified the sciences (understood them as “rationally ordered knowledge”) in (preliminary) instrumental knowledge (logic - proof, rhetoric-persuasion, poetics-beauty); in theoretical knowledge (physics, math & metaphysics); in practical knowledge (ethics, politics, and economics) and in productive order (techne or “know how”, the knowledge for producing or making).
Aristotle ranked these sciences as (1) theoretical — (2) practical — (3) productive (our “techie” society in reverse order). Practical knowledge should be more important because it is closer to home: it perfects our lives; theoretical knowledge should be ranked highest because it perfects our very essential selves, our souls, and our minds; it expands our consciousness, not just our world or behavior.

Sophism

Main claim: Man is the measure of all things. Truth and goodness were invented by and relative to subjective human minds and wills, whether individually or socially. Sophists are skeptics in epistemology, relativists in ethics, and subjectivists in both. The big idea of their ethic relativism considered that morality is not natural (created by God) but conventional (invented by humans). In epistemology, they were skeptics. They taught that we cannot attain knowledge of objective truth, only subjective opinions; that we cannot know reality, only appearances. For them “image is everything” since all we could know were appearances or images.

Main philosophers: Protagoras, Gorgias, Machiavelli.

Background: They were itinerant educators who taught their “wisdom” for high fees to rich Athenians in the fifth century BC. Their “wisdom” consisted mainly of clever tricks of rhetoric (Rhetoric: the art of persuading by speech). This was a necessary survival skill for the rich in Athens, given the invention of democracy and jury systems. Both demanded demagoguery (the “augury” or power to persuade the demos or masses). They had a famous advertisement: “We can make the weakest argument the strongest.”

Contributions:

They turned the interests of philosophers from science to ethics; from the cosmos to man; from physical facts to human values; from metaphysics and cosmology to anthropology, epistemology, ethics, and politics.
They developed methods of logical argumentation like the technique of “dialectical” arguing or arguing for both sides of an issue.
By their skepticism and relativism, they drew a line in the sand: they posed the challenge of demanding a response: a clearer and stronger argument for the traditional belief in objective truth and values.

Refutation:

Epistemological and moral relativism are self-contradictory:

For Sophists everything is true and it is not possible to think what is false. But, if every opinion is true, so is the opinion that not every opinion is true. If no opinion is false, neither is the opinion that some opinions are false.
Science, in fact successfully, has come to know many objective and universal truths.
Moral relativism ignores conscience, which always speaks with absolute authority. Even people who believe it is impossible to know any other universal laws usually still believe it is always wrong to disobey their own individual conscience. So, even relativists have one absolute.
It also seems to violate the Golden Rule. We all want others to respect our rights and to give justice — in other words, not to practice moral relativism.
It seems to destroy social bonds, and thus society itself, for keeping promises is a minimum requirement for all social bonds. Absent this moral bond, only external, physical force can hold a society together — think totalitarianism, tyranny, or dictatorship.
Moral relativism is boring. It makes heroism impossible. Moral relativists cannot write great stories.
Plato also thought that it makes you unhappy, for it undermines virtue, which is to the soul what health is to the body.

Skepticism

Main claim: Nobody knows anything real. Value judgments are uncertain. The terms “skepticism” and “relativism” are usually used interchangeably. But skepticism is in a sense the exact opposite of relativism, for it says that no one has the truth, while relativism says that everyone has it.

Main philosophers: Phyrro of Ellis, Montaigne, Hume

Refutation: Skepticism is self-contradictory in many ways:

Universal skepticism is not universally skeptical: It is not skeptical of itself.
If all opinions are equal, what about the opinion that all opinions are equal?
If all truth is only subjective, is that truth subjective too?
Is relativism absolute?
Must we be dogmatic about not being dogmatic?

Stoicism

Main claim: Happiness is always internal, and no amount of external things can, in fact, make us deeply happy - the “principle of apperception”; nothing is either good or bad, but thinking makes it so; there are things that are within our power and things outside our power; the result of wisdom is inner freedom; control of emotions, pain endurance, and inconvenience without complaint, believe in fate, and take moral virtue and honor very seriously.

Main philosophers: Epictetus, Seneca, Marcus Aurelius.

Refutation — Each of its main “up” points has a “downsize”:

If “there is no either good or bad, but thinking makes it so”, then thinking cannot discover any real goods or evils, and morality must be merely subjective, even though it is subjective and rational. This weakens morality rather than strengthens it.
We can indeed always actively choose our attitude but are we not also inevitably passive to pain, disease, bad fortune, and death?
Indifference to the suffering of others is more obviously bad than indifference to our own suffering is good.
It so emphasizes the acceptance of what we cannot change that it radically de-emphasizes what we can change and minimizes hope, effort, and optimism (is it better to endure a disease or to spend effort trying to cure it?)