Rafael. The School of Athens.

Plato stands center left, next to Aristotle.

Philosophy (from Greek philos "brotherly love" + sophia "wisdom") is the study of fundamental problems. Like science, philosophy is abductive; it does not find truth, but explanation.

Philosophy is something intermediate between theology and science. Like theology, it consists of speculations on matters as to which definite knowledge has, so far, been unascertainable; but like science, it appeals to human reason rather than to authority, whether that of tradition or that of revelation. All definite knowledge -- should I should contend -- belongs to science; all dogma as to what surpasses definite knowledge belongs to theology. But between theology and science there is a No Man's Land, exposed to attack from both sides; this No Man's Land is philosophy.

—Bertrand Russel, A History of Western Philosophy


1   Function

Philosophy is important because without it how would we ever debate whether or not philosophy is important?

People who think philosophy is useless also tend to think that society does not need to change. If you want to maintain the status quo, teaching people to question everything is a pretty stupid thing to do.

2   Structure

Philosophy consists of: axiology, epistemology, logic, metaphysics, philosophy of language.

Metaphysics studies definitions and paradigms. Some problems include the nature of existence, the definition of life, the nature of reality (the universe may be different outside of our senses), and categories of being (these are things which cannot be defined, for example the sensation of seeing red).

3   Philosophers

3.1   Diogenes the Cynic

Diogenes was ...

After being captured by pirates and sold into slavery, Diogenes eventually settled in Corinth. There he passed his philosophy of Cynicism to Crates, who taught it to Zeno of Citium, who fashioned it into the school of Stoicism, one of the most enduring schools of Greek philosophy.

4   Further reading


5   History

Philosophy began in Greece in the six century BC. After running its course in antiquity, it was again submerged by theology as Christianity rose and Rome fell. Its second great period, from the eleventh to the fourteenth centuries, was dominated by the Catholic Church, except for a few great rebels. This period was brought to an end by the confusions that culminated in the Reformation. The third period, from the seventieth century to the present day, is dominated more than either of its predecessors, by science; traditional religious beliefs remain important, but are felt to need justification, and are modified whenever science seems to make this imperative. [2]

Social cohesion and individual liberty are in a state of conflict or uneasy compromise throughout the whole period. In Greece, social cohesion was secured by loyal to the City State; even Aristotle, though in his time Alexander was making the City State obsolete, could see no merit in any other kind of polity. The degree to which the individual's liberty was curtailed by his duty to the City varied widely. In Sparta he had as little liberty as in Fascist Germany or Communist Russia; in Athens, in spite of occasional persecutions, citizens had, in the best period, a very extraordinary freedom from restrictions imposed by the state. Greek thought down to Aristotle is dominated by religious and patriotic devotion to the City; its ethical systems are adapted to the lives of citizens and have a large political element. [2]

When the Greeks became subject, first to the Macedonians and then to the Romans, the concepts appropriate to their days of independence were no longer applicable. This produce a more individual and less social ethic. The Stoics thought of the virtuous life as a relation of the soul to God, rather than as a relation of the citizen to the state. They thus prepared the way for Christianity, which, like Stoicism, was originally unpolitical. [2] Social cohesion, during the six and a half centuries from Alexander to Constantine, was secured, not by philosophy and not by ancient loyalties, but by force, first that of armies then that of civil administration. [2]

The barbarian invasion put an end, for six centuries, to the civilization of western Europe.

The three father of Western philosophy are Socrates, Plato, and Aristotle. All philosophers before them are lumped under one heading: the "pre-Socratics". [4]

In the ancient world, philosophy and science blurred together because nobody could conduct rigorous tests in those fields. Similarly, in modern times, we still philosophize a great deal about mind because the tools of neuroscience are lacking. [4]

Thus, the first person we called a philosopher, Thales of Miletus, was really a physicist and astronomer, except that he had no scientific method or scientific instrument, so he had to philosophize his way to conclusions about the physical world. [4] Thales was one of the first people in recorded history to seek natural explanation for natural events. [4] He thought the Earth floated on water, and the earthquakes result when waves rocked the earth. [4]

After seeing some moisture turn into air, slime, and earth, he came to believe there was an original substance from which all else is formed — an arche — and that this arche was water. [4]

He is famous for predicting a solar eclipse in 585 B.C., though he probably borrowed this skill from the Babylonians, who had been predicting eclipses for hundreds of years. [4]

What historians think is unique about Thales is the universality of his approach. Thales sought universal, rational, natural explanations for the world instead of mythological ones. That is why we call him the first philosopher. [4]

Anaximander (610-546 B.C.) was even more insistent to explain everything in terms of physical forces, and may also have been the first philosopher to write down his ideas, and the first to conduct a scientific experiment.

He believed the arche was an infinite, indefinite mass (apeiron) from which everything came, much like the primordial Chaos of Greek mythology. This was perhaps an improvement on Thales’ view that water was the original element, for water cannot account for the diversity of nature. For example, water is only wet and never dry. So the arche must be more basic than water, fire, earth, or air. [4]

Anaximander thought the earth we observe is the flat top of a cylinder, floating still in a vast void. He took note of fossils and proposed that animals had originally come from the sea, and humans had come from those animals. But he had no concept of natural selection. [4]

Anaximenes (585-528 B.C.) continued to seek natural, unifying explanations. He proposed the arche was air, and that things varied only in their density. Fire was diffused air, while water was condensed air, and earth was air condensed further still. [4]

Perhaps he rejected Anaximander’s apeiron proposal because the notion of an indefinite, unlimited substance is unintelligible to us, and is really no better an explanation than an origins myth involving gods and chaos, as described by the poet Hesiod (8th century B.C.). Anaximenes may have proposed air as the arche because it is intelligible and observable, and seems like it could be in everything, including rocks and trees and people. [4]

Xenophanes (b. 570 B.C.) followed the Milesian School and believed all things were made of earth and water. He may be best known as a critic of polytheism, writing: "Mortals deem that gods are begotten as they are. The Ethiopians make their gods black and snub-nosed; the Thracians say theirs have blue eyes and red hair." [4] Following several arguments, he concluded that God is one, eternal, non-anthropomorphic being. For Xenophanes, God is not much of a person, but rather the arche. [4]

Pythagoras (late 6th century B.C.) was born on the Greek island of Samos. He traveled widely and then settled in Southern Italy, where he founded a society of disciples. After his death, magical powers were attributed to him and a religion formed. Among its commands were to not eat beans, to not step over crossbars, and to not look in mirrors near a light. [4]

The Pythagoreans often attributed their own views and innovations to their founder, so it is easier to say what the Pythagoreans believed than to say anything about Pythagoras himself. The Pythagoreans, then, said that “all is number,” by which they meant that number was in everything. They had discovered the mathematical nature of music and harmony, and the numbers inherent to many shapes. Of course, they are best known today for the Pythagorean Theorem about right-angle triangles. [4]

Their most important influence was on Plato, and through Plato, on all of Western philosophy. Pythagoreans had a mystical reverence for the perfection of abstract mathematical thinking, and deemed it a firm foundation for philosophy. This confidence lay at the heart of Plato’s philosophy, as did the Pythagorean notion of a perfect, eternal world revealed to our minds but not our senses. [4]

The Pythagoreans also defended the immortality of the soul, though they believed that after physical death the soul did not travel to an alternate world, but returned to the present one in a different body, and not necessarily a human one. Pythagoras himself said he could remember fighting as a hero centuries earlier at the siege of Troy. [4]

5.1   The Pre-Socratics

The pre-Socratics generally speculated only on metaphysics.

Philosophy began with the pre-Socratic philosophers, the first of which were from Miletus on the Ionian coast of Asia Minor: Thales, Anaximander_, and Anaximenes_. These philosophers invented critical rationality; the theories they advanced were not offered as gospels or to be accepted on divine or human authority, but as rational products to be accepted or rejected on the basis of evidence and argument. [3]

Before these philosophers, people relied on mythology to explain what they saw around.

This first philosopher was Thales. None of his work, like the rest of the pre-Socratics, survives. But Plato and Aristotle mention him in their works, and that's how we know about him.

Thales of Miletus was active around 585 BC. [2] According to Aristotle, Thales thought that everything was made of water.

Anaximander_ was the second philosopher of the Milesian school.

It presumably seems better, indeed only right, to destroy even what is close to us if that is the way to preserve the truth. And we must especially do this when we are philosophers, [lovers of wisdom]; for though we love both the truth and our friends, piety requires us to honour the truth first.

—Aristotle, Nicomachean Ethics

5.1.2   Heraclitus and Parmenides

Heraclitus (535-475 B.C.) of Ephesus thought the world was unified by a kind of harmony that resulted from strife between opposites: health and illness, good and evil, day and night. The world, he thought, was dominated by a cosmic justice that prevented one opposite from overcoming the other. [4]

He was the most pithy and quotable of the pre-Socratics. Among his one-liners are: “Donkeys prefer straw to gold” and “Man’s character is his fate” and “Swine wash in the mud, and barnyard fowls in the dust.” Heraclitus was enamored with his own prose, and wrote as a prophet proclaiming the Word of Heraclitus. [4]

Heraclitus seems to have recognized the problem faced by the Milesian school: If the arche is unmoving and eternal, then how do we explain the leap from unmoving being to the dynamic becoming we see all around us? Heraclitus’ solution was to remove being altogether. He said that everything is always changing: “You cannot step into the same river twice, for new waters are ever flowing in upon you.” [4]

Parmenides (510-440 B.C.) of Elea offered the opposite solution. He rejected becoming altogether in favor of motionless being. He thought that nothing ever changes. Our senses give us nothing but illusion, and everything is really The One — a kind of perfect sphere that cannot be divided. Everything that exists has always existed and will always exist. [4] This doctrine is similar to the "block universe" theory of modern physics, according to which time does not "flow" but instead the past and present and future all exist, but in different directions, like backward and forward. Arguing against this theory, Karl Popper exclaimed to Einstein, "You are Parmenides!" [4]

More important than Parmenides’ metaphysical claim itself is that he gave an argument for it. He appears to have argued something like this: When you think and speak, you think and speak about something. But you can think and speak about some thing at one time as well as another. So whatever you can think and speak of must exist at all times. So there can be no change, for change consists of things beginning to be or ceasing to be. [4]

This argument is obviously flawed, for we often use words to speak of things that do not exist (unicorns) or things from the past (Shakespeare) or the potential future (interstellar spacecraft). [4]

Because he initiated the purely rational method of inquiry about reality, and therefore opened the debate between rationalism and empiricism that would later dominate so much of the history of philosophy, and because he was the first epistemologist in that he clearly distinguished belief from knowledge, Parmenides is often named the most important philosopher before Socrates. [4]

Heraclitus and Parmenides mapped the battlefield for centuries of philosophical struggle. It was of central importance to Democritus, Plato, Aristotle, and others to reconcile being and becoming. [4]

Parmenides was an ancient Greek philosopher. He contributed to ontology. He was the founder of the Eleatic school of philosophy In 'the way of truth' he explains reality is one, change is impossible, and existence is timeless, uniform, necessary, and unchanging

Like Parmenides, Melissus argued that reality is ungenerated, indestructible, indivisible, changeless, and motionless.

5.1.3   Zeno of Elea

Zeno of Elea (490 - 430 BC) is today best known for his paradoxes_. His arguments may be the earliest examples of `reductio ad absurdem`_. Zeno used several such arguments in defense of Parmenides' doctrine that change is impossible. [4]

Of Zeno's nine surviving paradoxes, two are of most interest. They are Achilles and the tortoise, and the flying arrow.

The paradox of Achilles and the tortoise goes like this: Achilles and the tortoise are in a footrace, and Achilles gives the tortoise a head start of, say, 100 meters. Both start running at a constant speed, with Achilles running faster than the tortoise. After some time, Achilles will have run 100 meters and caught up to the tortoise’s starting point, and in the meantime the tortoise will have progressed some shorter distance: say, 10 meters.

It then takes Achilles some time to cross those 10 meters, by which time the tortoise will have moved a bit further ahead. And so on. So whenever Achilles reaches the point where the tortoise was most recently, he still has further to go! And so Achilles can never catch up with the tortoise. And yet experience tells us that Achilles can easily pass the tortoise. Hence the paradox.

The flying arrow paradox arises from divisions of time rather than divisions of space. Zeno notes that for motion to occur, an object such as a flying arrow must change positions. In any given instant of time, for the arrow to be moving it must either move to where it is, or move to where it is not. But it cannot move to where it is not, because we are considering only a single instant of time. And it cannot move to where it is, because it is already there. Thus at any given instant of time, the arrow is not moving. Therefore the arrow cannot move at any instant of time, meaning it cannot move at all. [4]

Moreover, Zeno may have been the first person to practice the “dialectic” made famous by Socrates: that practice of two or more people exchanging arguments and counter-arguments, ending in a refutation of one view or perhaps a synthesis of both views. [4]

5.1.4   Empedocles

Empedocles (490-430 B.C.) is perhaps best known for two scientific discoveries involving buckets. First, he noticed that if you push an upside-down bucket under water, the water does not rush in to fill the bucket. Thus, he discovered that air is its own, separate substance. Second, he noticed that if you swing a bucket of water around on a rope above your head, the water does not fall out of the bucket. Thus, he discovered centrifugal force. [4]

Empedocles thought that the original elements were earth, fire, air, and water, which when combined in different ways result in everything we see. But there must be active forces that cause these elements to be combined in various ways, and these forces are Love and Strife. Despite their names, Empedocles thought of these as physical forces: Love attracted elements together to form objects, and Strife pushed them apart and decayed objects. This cycle proceeded by chance and physical necessity rather than by cosmic purpose. [4]

5.1.5   Anaxagroas

Anaxagoras (500-428 B.C.) brought philosophy to Athens.

The exception is mind (nous), which exists only in living things, and is the cause of all motion. Aristotle complained that Anaxagoras tried to offer a natural explanation for everything, except that whenever he couldn't explain something he put “mind” into the gap. Anaxagoras proposed a "mind of the gaps" just as many theologians proposed a "God of the gaps." [4]

Anaxagoras was eventually banished from Athens. [4]

5.1.6   Democritus

Democritus (b. 460 B.C.) prefigured the findings of modern science most completely. He believed that everything is made of atoms that are physically indivisible, that there is empty space (void) between atoms, that atoms are always in motion, that atoms are indestructible, and that there are many kinds of atoms. [4]

According to him, atoms form different substances based on their shape. Iron holds together firmly because its atoms have hooks. Water flows because its atoms are smooth and slippery. Salt has a sharp taste because its atoms are pointy. [4]

Democritus was a strict determinist. He did not believe in chance, but rather thought that everything proceeded due to natural laws. Even thought and the soul were made of atoms and governed by natural laws. [4]

Democritus was also the first philosopher to offer a systematic morality. Happiness was to be found in a life of cheerfulness and quiet contentment. Moderation is good, but asceticism is not. The trick is to choose the right times for fasting and feasting. In placing happiness at the center of ethics, Democritus set the agenda for many Greek ethical systems to come. But he did not mention that other ground of Greek ethics: virtue. [4]

5.1.7   Eubuilides

Eubuilides of Miletus was a philosopher of the Megarian school and contemporary of Aristotle. He is famous for several paradoxes:

  1. The Liar paradox: A man says: "What I am saying now is a lie." If the statement is true, then he is lying, even though the statement is true. If the statement is a lie, then he is not actually lying, even though the statement is a lie. Thus, if the speaker is lying, he tells the truth, and vice versa.

  2. The Masked Man paradox: "Do you know this masked man?" "No." "But he is your father. So - do you not know your own father?"

  3. The Sorites paradox

  4. The Bald Man paradox:

    Would you describe a man with one hair on his head as bald? Yes. Would you describe a man with two hairs on his head as bald? Yes. ... You must refrain from describing a man with ten thousand hairs on his head as bald, so where do you draw the line?

5.3   Epicurus

Epicurus was an ancient Greek philosopher who during the 4th century BC founded the school of philosophy called Epicureanism which claims that the aim of human life is pleasure.

Epicurus was born in 341 in Samos. He was a student under a follower of Democritus. At 18, he moved to Athens for two years of compulsory service. At 34, he bought a house and garden and set up a philosophical community of friends; his school became known as "The Garden". He never married. He wrote on diverse topics such as ethics, physics, astronomy, language, and epistemology.

Pleasure is the only thing which is good in itself and the criterion by which we judge things.

Many of Epicurus' complete works have survived. We have several letters he sent to friends which summarize his major teachings. He was cited in full by `Diogenes Laertius`_. We also have works by followers including Lucretius. Also have a library once owned by a wealthy Roman senator which was covered in an eruption which preserved scrolls containing the text of Epicurus. Also have an enormous wall in southwest Turkey inscribed with Epicurean teachings which survived in fragments.

Epicurus' physics said things are either a body or void. Our senses tell us there are bodies and void, since there must be to have motion. Since we see things around change, those things can't be fundamental but must be made up of enumerable fundamental parts. Space must be infinite since what would mark the end. There must also be an infinite number of atoms. Hit on a problem of a free will if everything is determined. Democritus thought everything determined by the laws of physics. Epicurus disagreed, since it conflicted with experience and would make morality impossible. He introduced the notion of "the swerve": an atom at any time may veer off its give path very slightly which gives overwhelming regularity but makes the laws of physics insufficient for explaining free will. (Though, it's unclear if atomic indeterminacy helps explains free will. This discussion was revived with when `Werner Heisenberg`_ introduced his `uncertainty principle`_ which proved Epicurus right.)

Epicurus thought even the soul was composed of bodies and void. He asserted that the causes of sensations could not be sensations themselves, and hypothesized that atoms had an atomic film that would float off and enter into the sense organs which would convert them into percepts. Percepts are true, but they may not be the in the same state as when they left the atom and so may require some interpretation.

Most Ancient Greek philosophers were skeptics. Epicurus relies on the senses to know there are bodies and movement, but many skeptics distrust senses because two sense impressions conflict. For example, with a straw looking bent when partially submerged in water. Epicurus would argue these are not really conflict- it does really look bent but it also does really feel another way.

Epicurus did not give a definition of pleasure, but thought it was an intuitive notion that every human from birth recognizes as the good just as we recognize that fire is hot and snow is cold. Epicurus was interested in the different kinds of pleasures and their relative values.

  • Kinetic pleasures are positive sensory stimulation.
  • Static pleasures are the removal of pain, for example quenching thirst or not being hungry or cold.
  • Mental pleasures are superior because we can enjoy past and future pleasures. Mental painlessness is the highest state of pleasure.

Epicurus thought that we cannot enhance pleasure with luxuries, but only vary the pleasure. The height of pleasure is achieved when all pain is gone.

We can only obtain pleasure by understanding the nature of things and gods. Virtues are good as a mean to the life of tranquility and help us deal with pain and suffering. This was a very disciplined life.

Friendship is a source of mental pleasure but conflicts with the idea of living a painless life because friendship sometimes require pain.

Epicurus had the idea of "Tetrapharmakos" or "four-part remedy". Philosophy is the medicine of the soul. As expressed by Philodemous, the tetrapharmakos reads:

Don't fear god, Don't worry about death Good is easy to get, Pain is easy to endure

The explanation is as follows:

  1. Either the gods must be happy or they must be concerned with people, but they must be happy since they are blessed.
  2. The soul is made of atoms. Therefore there is no surviving after death, only nonexistence, and nonexistence can't be experienced so there is nothing to worry about.
  3. Good can be attained by satisfying natural and necessary desires.
  4. Pain can be endured through various strategies, such as reliving past memories. Severe pains do not last long because they will kill you.

Many people perceived the Epicurean school to be conservative and unadaptive. However, it survived into Rome with the Epicurean philosopher Philodemus who set up a school at a leisure spot of wealthy Romans.

Lucretius was the most important philosopher of Lucretius who reportedly treated Epicurus as a god. It was through Lucretius that the Renaissance discovered Epicurus.

This reminds me of the sword of Damocles.

Cicero asks, "Does not Dionysius seem to have made it sufficiently clear that there can be nothing happy for the person over whom some fear always looms?"

5.4   Stoicism

Stoicism came a generation after Epicureanism and became a major competitor. It different on all major topics.

5.6   Linguistic turn

Frege is generally considered one of the most important philosophers of the 19th century. Among other things, he is credited with catalyzing what noted philosopher Richard Rorty called the “linguistic turn” in philosophy. As Enlightenment philosophy was obsessed with questions of knowledge, philosophy after Frege became obsessed with questions of language. His disciples included two of the most important philosophers of the 20th century—Bertrand Russell and Ludwig Wittgenstein. [5]

The major innovation of Frege’s logic is that it much more accurately represented the logical structure of ordinary language. Among other things, Frege was the first to use quantifiers (“for every,” “there exists”) and to separate objects from predicates. He was also the first to develop what today are fundamental concepts in computer science like recursive functions and variables with scope and binding. [5]

Frege’s formal language — what he called his “concept-script” — is made up of meaningless symbols that are manipulated by well-defined rules. The language is only given meaning by an interpretation, which is specified separately (this distinction would later come to be called syntax versus semantics). This turned logic into what the eminent computer scientists Allan Newell and Herbert Simon called “the symbol game,” “played with meaningless tokens according to certain purely syntactic rules.” [5]

As Bertrand Russell famously quipped: “Mathematics may be defined as the subject in which we never know what we are talking about, nor whether what we are saying is true.” [5]

6   Remarks

7   Further reading

8   References


How to study philosophy as an amateur.

This resource also includes many links for further reading about specific philosophers.

[2](1, 2, 3, 4, 5) Bertrand Russel. 1945. The History of Western Philosophy.
[3]C.D.C. Reeve. (Professor of Philosophy at Reed College). Ionian Thinkers.
[4](1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38) Luke Muehlhauser. Pre-Socratics: A Painless Introduction.
[5](1, 2, 3, 4) Chris Dixon. March 20, 2017. How Aristotle Created the Computer.


There are two major hurdles when trying to get into philosophy: The Principle of Charity, and that almost every text requires context (since 1) almost every text was written as a response to someone else, 2) a lot of the major philosophical works are written for other philosophers, to convince those peers of radical new ideas, and 3) works of philosophy use specialized vocabulary e.g. a prior, a posterior, deontology, consequentialism, utilitarianism, empiricism, subjective, objective, espistemology, ontology, metaphysics, aesthetics, metaethics, analytic/synthetic).

It can be difficult to understand what someone means, or why they would think a certain thing, if you lack the context about who they are responding to and the general philosophical climate that they were working in.


First off, there is really only one thing to keep in mind when reading a philosophical text, and it's the thing that seems to be the most lacking in new readers: The Principle of Charity. It asks that you read a text in the strongest, most persuasive way possible, regardless of whether you agree with the content. This is extremely important for reading philosophical texts, because many of them will challenge your ideals. Some might even say that is the entire point of reading philosophy, so if you fail in the Principle of Charity, you fail at reading philosophy entirely.

Everyone thinks the principle is great in general. However, no one thinks that they themselves need to follow it more, no matter how much they turn everything they don't agree with into a straw man. If you showed Glenn Beck the Wikipedia page for the Principle of Charity, he would probably say: "That's great, I couldn't agree more! Liberals need to be more charitable with conservative arguments. I, however, am perfectly charitable with their arguments - their arguments are just bad". In that way it's very similar to the Dunning-Krugar effect; in a rather self-fulfilling way, no one seems to think it applies to themselves.

So I am proposing a new principle: The Principle of Science. When first reading a philosophical text, you should read it not as the most compelling argument, but rather as though you were reading a scientific text. The reason for this is simple: scientific texts are taken as fact. Philosophy texts are always presumed to be questionable. When you first encounter Newton's Law that says an object in motion will continue in motion until acted upon, you don't say, "What a load of crap, I threw a meat pie at my cousin Mike just last week, and it stopped on its own accord before it got to him." Obviously, although scientific theories can be overturned, people assume that they are correct, so their only objective becomes trying to understand the theory. However, when Kuhn says that science, like evolution, progresses towards nothing in particular, a lot of people's first reaction is something like: "What a load of shit, science obviously progresses towards the truth", then they spent the rest of the time trying to work out just how wrong Kuhn is. Now, obviously Kuhn's claim is much more controversial than Newton's, and in fact most philosophers don't agree with him, but the point of reading his book shouldn’t necessarily be to become a Kuhnian, but rather to understand him. That doesn't mean that you can’t critique the ideas afterwards, but understanding the ideas first is much more important than refuting them, and you really shouldn't worry about it too much.

There is a fun fact that if you click on the first link in the main text of a Wikipedia article, and then repeat that on each following article, you eventually get to Philosophy, though this is apparently only true 94.52% of the time. Nonetheless it suggests that all knowledge can be arranged hierarchically underneath the general heading of "Philosophy".

When people question the value of philosophy and literature, remember: it's the first thing dictators purge. They seem to know the value.

We must challenge the thought that philosophy aims to contribute to human knowledge of the world. Its task is to resolve philosophical problems. The characteristic feature of philosophical problems is their non-empirical, a priori character: no scientific experiment can settle the question of whether the mind is the brain, what the meaning of a word is, whether human beings are responsible for their deeds (i.e. have free will), whether trees falling on uninhabited desert islands make any noise, what makes necessary truths necessary. All these, and many hundreds more, are conceptual questions. They are not questions about concepts (philosophy is not a science of concepts). But they are questions that are to be answered, resolved or dissolved by careful scrutiny of the concepts involved.

The only way to scrutinise concepts is to examine the use of the words that express them. Conceptual investigations are investigations into what makes sense and what does not. And, of course, questions of sense precede questions of empirical truth – for if something makes no sense, it can be neither true nor false. It is just nonsense – not silly, but rather: it transgresses the bounds of sense. Philosophy patrols the borders between sense and nonsense; science determines what is empirically true and what is empirically false. What falsehood is for science, nonsense is for philosophy.

Let me give you a simple example or two. When psychologists and cognitive scientists say that it is your brain that thinks rather than nodding your head and saying, “How interesting! What an important discovery!”, you should pause to wonder what this means. What, you might then ask, is a thoughtful brain, and what is a thoughtless one?

Can my brain concentrate on what I am doing, or does it just concentrate on what it is doing? Does my brain hold political opinions? Is it, as Gilbert and Sullivan might ask, a little Conservative or a little Liberal? Can it be opinionated? Narrow-minded? What on earth would an opinionated and narrow-minded brain be? Just ask yourself: if it is your brain that thinks, how does your brain tell you what it thinks? And can you disagree with it? And if you do, how do you tell it that it is mistaken, that what it thinks is false? And can your brain understand what you say to it? Can it speak English? If you continue this line of questioning you will come to realise that the very idea that the brain thinks makes no sense. But, of course, to show why it makes no sense requires a great deal more work.

So, why study philosophy?

There are many reasons, and many different kinds of reason. At a very general level, it is a unique technique for tackling conceptual questions that occur to most thinking people: questions concerning the existence of God, of an afterlife, and of free will. Also questions concerning human nature: what is the mind? How is the mind related to the body? Do we have a soul?

The study of philosophy cultivates a healthy scepticism about the moral opinions, political arguments and economic reasonings with which we are daily bombarded by ideologues, churchmen, politicians and economists. It teaches one to detect ‘higher forms of nonsense’, to identify humbug, to weed out hypocrisy, and to spot invalid reasoning. It curbs our taste for nonsense, and gives us a nose for it instead. It teaches us not to rush to affirm or deny assertions, but to raise questions about them.

As Alexander the Great was passing through Corinth, he sought out Diogenes and finally found him sitting under a tree, dressed in rags, with not a drachma to his name. When the most powerful man in the world asked the philosopher if he could do anything to help him, Diogenes replied, "Yes, if you could step out of the way. You are blocking the sun." Alexander laughed, and remarked that if he were not Alexander, he would certainly like to be Diogenes.

A well travelled man could have met Socrates, Confucius and Buddha.

I like the idea of a "mental knot"

"My attempt to summarize Nietzsche in a thought experiment: Imagine you were going to live this same life again and again for eternity. How would that change your behavior?"