Aristotle: 'All Human Beings by Nature Desire to Know' — The Master of Those Who Know Who Classified and Systematised the World

Key Takeaways

• The Four Causes and Hylomorphism: Aristotle explained every instance of being and change through four causes — material, formal, efficient, and final. Each individual thing is a composite (synolon) of form and matter; essences do not exist separately as Plato's Forms but inhere in concrete particulars. This framework profoundly influenced the methodology of the natural sciences.
• Logic (the Organon) and the Syllogism: Aristotle was the first to systematise formal logic, formulating the syllogism (syllogismos) as the basic pattern of valid inference. His logic remained the intellectual foundation of the West for over two thousand years, until Frege inaugurated predicate logic in the nineteenth century.
• The Doctrine of the Mean and Eudaimonia: The highest good for human beings is happiness (eudaimonia), which is realised through the activity of the soul in accordance with virtue. Virtue is a settled disposition lying at the mean (mesotēs) between excess and deficiency, and it is acquired through habit and practice.

Life and Historical Context

Aristotle was born in 384 BCE in Stageira, a small town on the northern edge of the Macedonian kingdom. His father Nicomachus was the personal physician of King Amyntas III of Macedon. The fact that he was born into a family of physicians helps account for his empirical, observation-oriented intellectual temper (Diogenes Laërtius, Lives of the Eminent Philosophers V.1).

At the age of seventeen (367 BCE) Aristotle travelled to Athens and enrolled in Plato's Academy. He remained there for twenty years, until Plato's death in 347 BCE. Plato reportedly called Aristotle "the intellect of the school" (nous) (Diogenes Laërtius V.1), and the relationship between master and pupil was at once intimate and intellectually tense. Aristotle himself later wrote — in the spirit summarised by the Latin tag amicus Plato, sed magis amica veritas — "Plato is a friend, but truth is a greater friend" (cf. Nicomachean Ethics I.6, 1096a16).

After Plato's death Aristotle left Athens and continued his research at Assos in Asia Minor under the protection of the tyrant Hermias. During this period he married Pythias, Hermias' adopted daughter (or, by some accounts, niece), and had a daughter of the same name (Diogenes Laërtius V.1). When Hermias was captured and executed by the Persians, Aristotle moved to the island of Lesbos, where he and his pupil Theophrastus devoted themselves to detailed observation and recording of animal and plant life. The research carried out there bore fruit in the History of Animals (Historia Animalium), Parts of Animals, and Generation of Animals, which together constitute a pioneering achievement in empirical natural science. In 343 BCE he was summoned by King Philip II of Macedon to serve as tutor to the young prince Alexander — the future Alexander the Great. The encounter between philosopher and conqueror is one of history's ironies, but much about the intellectual influence each exerted on the other remains unknown.

In 335 BCE Aristotle returned to Athens and established his own school in the Lyceum (a precinct sacred to Apollo Lykeios). Because he and his pupils discussed philosophy while walking along the covered walkway (peripatos), the school became known as the Peripatetic School. Here Aristotle devoted twelve years to lecturing, research, and writing. The bulk of his surviving works are believed to derive from lecture notes of this period.

In 323 BCE, when Alexander the Great died suddenly, anti-Macedonian sentiment surged in Athens. Facing the threat of a charge of impiety, Aristotle withdrew to Chalcis, remarking that he would not allow the Athenians "to sin twice against philosophy" — a pointed allusion to the execution of Socrates. He died the following year, in 322 BCE, at the age of sixty-two (Diogenes Laërtius V.5–10).

Mini-Timeline

• 384 BCE: Born at Stageira. His father is physician to the king of Macedon
• 367 BCE: Travels to Athens aged seventeen. Enrols in Plato's Academy
• 347 BCE: Plato dies. Aristotle leaves the Academy for Assos
• 345–343 BCE: Conducts biological research on the island of Lesbos
• 343 BCE: Appointed tutor to Alexander
• 335 BCE: Returns to Athens. Founds the Lyceum
• 323 BCE: Alexander the Great dies. Aristotle withdraws to Chalcis
• 322 BCE: Dies at Chalcis (aged 62)

What Did This Philosopher Ask?

Plato posited eternal, unchanging Forms behind the world of the senses. The individual horses and flowers we see around us were held to be merely imperfect copies of a perfect "Form of Horse" or "Form of Flower" existing in a transcendent realm. Aristotle, however, raised a fundamental objection: if "the Form of Horse" exists somewhere in the heavens, how does that explain why the horse before our eyes runs and grows? A Form separated from particulars, he argued, cannot serve as their cause (Metaphysics I.9, 990b–991b).

The core of Aristotle's inquiry was this: what is "being" (ti to on)? What does it mean for something to exist? Why do things change? How is knowledge possible? How should a human being live? His fundamental commitment was to answer these questions not by appealing to heavenly Forms but by starting from the empirical facts of the world around us.

It was thus that Aristotle conceived of what he called "first philosophy" — the discipline that investigates "being qua being" (Metaphysics IV.1, 1003a21). Natural philosophy studies the natural world; mathematics studies numbers and shapes; but first philosophy asks the most fundamental question of all: what does it mean for something to exist? It is the foundation on which every other science rests. Here begins Aristotle's grand system of knowledge.

Core Theories

1. Substance (ousia) — The Primary Meaning of Being

"Being is said in many ways" (Metaphysics IV.2, 1003a33) — this is Aristotle's starting point. When we say that something "is," the meaning is not uniform. "Socrates exists," "is white," "is three cubits long," and "is double" are all ways of being, yet each differs from the others. Aristotle sorted these different modes of being into categories (katēgoriai) — substance, quality, quantity, relation, and so on. His key insight is that all the other categories presuppose substance. For "white" to exist there must be some thing that is white — a white wall, a white sheet of paper. Colour and size do not float in the air on their own.

Aristotle gave substance a twofold specification. Primary substance is the individual concrete existent — "this human being," "this horse" (Categories 5, 2a11–19); secondary substance is the species ("human being") or genus ("animal"). Plato attributed primary reality to the universal (the Form); Aristotle reversed this entirely. Particulars are what is most real — this is the bedrock of Aristotle's metaphysics.

2. Form and Matter (Hylomorphism)

Every individual thing is a composite (synolon) of form (eidos/morphē) and matter (hylē). Take a bronze statue: the bronze is the matter; the shape of the statue is the form (Metaphysics VII.3, 1029a3–5). Form bears the same Greek name (eidos) as Plato's Form, but the decisive difference is that it does not exist separately from the individual — it inheres in the matter.

In living beings this framework becomes especially clear. The soul (psychē) is the form of the body, and the body is the matter of the soul (De Anima II.1, 412a19–21). Consider: the form of an eye is "the capacity to see"; the form of an axe is "the capacity to cut." In the same way, the soul is not a spiritual entity independent of the body; it is the "function" of the living body as a whole — the activity of nourishing, perceiving, and thinking. In Aristotle's technical language, it is the "first actuality" of a natural body. This way of thinking rejects the Platonic dualism that treats soul and body as separate entities, and can be seen as a forerunner of functionalism in the modern philosophy of mind — the view that the mind is what the body does.

3. The Four Causes — Exhausting the Question "Why?"

For Aristotle, "to know" is "to know the cause" (Physics II.3, 194b17–20). And there are four kinds of cause.

(1) The material cause (hylē) — that out of which a thing is made. The bricks and timber of a house. (2) The formal cause (eidos) — what a thing is. The blueprint of the house. (3) The efficient cause (archē tēs kinēseōs) — what brought it about. The builder who constructed the house. (4) The final cause (telos) — that for the sake of which. A house is built for the purpose of dwelling. These four causes are not independent of one another; they are four angles from which a single thing is explained. For a house to exist as a house there must be materials, a design, a builder, and a purpose — only when all four are specified has one fully answered "why this house exists."

For Aristotle, nature, too, works purposively: the acorn does not happen to become an oak — it grows in order to become one. Eyes exist for seeing; teeth exist for chewing. This teleology (from telos, "end") stands in sharp contrast to the mechanistic worldview of modern science, which explains natural phenomena by mechanical causation alone. Yet in biology the question "What is this organ for?" remains valid to this day. "Nature does nothing in vain" (Politics I.2, 1253a9) — this principle shows a structural affinity with the explanation of adaptation by natural selection.

4. Potentiality and Actuality (dynamis and energeia)

What is change? Parmenides denied change; Plato relegated it to the world of shadows. Aristotle resolved the problem through the distinction between potentiality (dynamis) and actuality (energeia) (Metaphysics IX.1–9).

An acorn is a potential oak tree; when it has grown into an oak it has reached actuality. Likewise, a block of marble contains the hidden potential to become a beautiful statue; when a sculptor gives it shape, it reaches actuality. In other words, change is the emergence of a latent possibility into manifest reality. Aristotle gave this a rigorous formulation: change is "the actualisation of what is potential qua potential" (Physics III.1, 201a10–11). The crucial point is that being is no longer a simple binary of "is" or "is not." By admitting an intermediate state — "not yet fully, but capable of becoming" — Aristotle avoided the paradox of generation from nothing that Parmenides had closed off, while giving a rational account of the change we witness every day: seeds sprouting, children growing into adults.

Moreover, Aristotle insists that actuality is prior to potentiality (Metaphysics IX.8). The hen is prior to the egg — the completed form is what the potential aims at and is ontologically prior. This principle leads to the summit of his cosmology: the Unmoved Mover.

5. The Unmoved Mover — Pure Actuality

Motion is eternal, Aristotle held. But the chain of movers requires an ultimate cause. Whatever moves something is itself moved by something else — and this series cannot regress to infinity. Therefore there must exist something that moves all other things without being moved itself — the "Unmoved Mover" (to prōton kinoun akinēton) (Metaphysics XII.7, 1072a23–b3).

The Unmoved Mover is pure actuality containing no potentiality. Whatever can change is still incomplete; the Unmoved Mover has no such incompleteness. It is "thinking of thinking" (noēsis noēseōs) — pure intellect eternally engaged in the activity of thinking itself (XII.9, 1074b33–35).

But how can something that does not move itself move the world? Aristotle's answer is striking. The Unmoved Mover moves the cosmos not by physical force but "as that which is loved" (XII.7, 1072b3). An analogy helps here: an admired person, without issuing a single command, inspires those around them to strive to become better versions of themselves. In the same way, the very existence of something perfect calls forth the aspiration of all things, which seek to realise themselves in its direction — a kind of teleological attraction pervading the universe. This concept exerted a decisive influence on medieval Christian theology, above all on Thomas Aquinas' proofs for the existence of God.

6. Logic — The Syllogism and the Instrument of Science

Aristotle regarded logic not as a branch of philosophy but as the "instrument" (organon) that precedes every science. His logical works — the Categories, De Interpretatione, Prior and Posterior Analytics, Topics, and Sophistical Refutations — were later collectively known as the Organon.

At the heart of the system stands the syllogism (syllogismos). "All human beings are mortal (major premise); Socrates is a human being (minor premise); therefore Socrates is mortal (conclusion)" — we reason like this every day without noticing it. Aristotle extracted this everyday reasoning into a formal pattern: "All M is P; all S is M; therefore all S is P." This pattern was identified as the basic unit of inference, and the valid forms of syllogism were exhaustively classified (Prior Analytics I.1–7). Kant remarked in the preface to the Critique of Pure Reason that Aristotle's logic "has not been able to advance a single step since, and is to all appearances a closed and completed body of doctrine" (Bviii). It was not until the nineteenth century, when Frege inaugurated predicate logic, that this two-thousand-year reign came to an end.

7. Ethics — The Doctrine of the Mean and Eudaimonia

Aristotle's ethics begins from happiness (eudaimonia). "Every art and every inquiry, and similarly every action and choice, is thought to aim at some good" (Nicomachean Ethics I.1, 1094a1–3). The good of goods — that which is sought for its own sake and is never a means to anything else — is happiness (eudaimonia).

What, concretely, is happiness? Aristotle defines it as "activity of the soul in accordance with virtue (aretē)" (I.7, 1098a16–17). Happiness is not a moment of pleasure or the possession of wealth; it is the lifelong practice of virtuous living. ("One swallow does not make a spring" — I.7, 1098a18.)

Virtue (ethical virtue) is a settled disposition (hexis) lying at the mean (mesotēs) between excess and deficiency (II.6, 1106b36–1107a2). Courage is the mean between recklessness (excess) and cowardice (deficiency); generosity is the mean between prodigality and stinginess. The mean, however, is not an arithmetical midpoint; it varies with the situation, the person, and the occasion — "at the right time, about the right things, towards the right people, for the right end, and in the right way" (II.6, 1106b21–23).

Importantly, virtue is not innate but acquired through habit (ethos) (II.1, 1103a14–26). Just as one becomes a lyre-player by playing the lyre, one becomes courageous by performing courageous acts. Ethics is a matter not of theory but of practice; knowing is not enough — one must act.

Such virtues are not perfected in the isolated individual. Aristotle placed great weight on the fact that the good life necessarily involves relationships with others, and he devotes two of the ten books of the Nicomachean Ethics (Books VIII–IX) to an analysis of friendship (philia). He distinguishes three kinds: friendship based on utility (relationships of mutual advantage, as in commerce), friendship based on pleasure (young people sharing enjoyment), and complete friendship based on virtue (wishing good for the other's own sake) (VIII.3, 1156a6–b6). Complete friendship presupposes that both parties are virtuous; it requires time and intimacy and is therefore rare, yet it is indispensable to the good life. "No one would choose to live without friends, even if he had all other goods" (VIII.1, 1155a5–6).

What, then, is the most happy way of living within a life of virtue? Aristotle's answer, given in the final book of the Nicomachean Ethics, is the contemplative life (bios theōrētikos) (X.7–8, 1177a12–1179a32). This is a life given over to the pure desire to understand the truths of nature and the cosmos — the pursuit of knowledge for its own sake. Contemplation is self-sufficient and sought for its own sake alone. It represents the highest form of intellectual virtue (dianoētikē aretē) and, together with the practical life grounded in ethical virtue, constitutes one of the two pillars of happiness. At the same time, Aristotle the realist acknowledged that external goods — health, wealth, friends — are to some degree necessary for happiness (I.8, 1099a31–b8). Neither pure spiritualism nor materialism, this sense of balance is itself characteristic of Aristotle.

8. Politics — "Man Is by Nature a Political Animal"

"Man is by nature a political animal" (zōon politikon) (Politics I.2, 1253a2–3), Aristotle declared. A human being cannot live well in isolation. It is by exchanging words, establishing laws, and debating justice and injustice within a community that we fulfil our nature as human beings. Ethics treats the happiness of the individual; politics treats the happiness of the community as a whole. Politics is thus the extension of ethics and "the most authoritative and architectonic science" (Nicomachean Ethics I.2, 1094a26–b7).

Aristotle collected and analysed the constitutions of 158 city-states (most of these are lost, but the Constitution of the Athenians survives) and classified constitutions by the number of rulers (one, few, or many) and their aim (the common good or private interest), yielding six types (Politics III.7). Correct forms: monarchy, aristocracy, and polity (politeia). Deviant forms: tyranny, oligarchy, and democracy. Aristotle considered a "mixed constitution" with a strong middle class the most stable form of government (IV.11) — here, too, the spirit of the mean finds its political application.

Guide to Key Texts

• Metaphysics (Ta meta ta physika) — Investigates "being qua being." Treats substance, cause, and the Unmoved Mover. Translation: W.D. Ross (Oxford, 1924); revised in J. Barnes (ed.), The Complete Works of Aristotle (Princeton UP, 1984).
• Nicomachean Ethics (Ēthika Nikomacheia) — Treats happiness, virtue, friendship, and the contemplative life. The masterpiece of Aristotle's ethics. Translation: Terence Irwin (Hackett, 2nd ed., 1999).
• Physics (Physica) — Treats motion, change, place, time, and infinity. A foundational text in natural philosophy.
• Politics (Politica) — Analyses the state and its constitutions. The wellspring of political science. Translation: C.D.C. Reeve (Hackett, 1998).
• De Anima (On the Soul) — Defines the soul as the form of the body. The origin of the philosophy of mind.
• Poetics (Peri Poiētikēs) — An analysis of tragedy. The theory of mimēsis (imitation) and katharsis (purification) laid the foundations of Western literary criticism.
• Prior and Posterior Analytics (Analytica) — The theory of the syllogism and of scientific demonstration. The starting point of formal logic.
• Rhetoric (Rhētorikē) — A systematic analysis of the art of persuasion. Treats the three means of persuasion — argument (logos), character (ēthos), and emotion (pathos) — and founded Western rhetorical theory.

Major Criticisms and Controversies

1. Critique of teleology: "Why does a stone fall?" — Aristotle would answer "because it tends toward its natural place (downward)," whereas modern science answers "because the force of gravity acts on it." Galileo and Newton banished the final cause from scientific explanation, and sought to explain nature primarily through mechanistic causation — above all through efficient-causal accounts. Bacon pronounced the search for final causes "barren, like a virgin consecrated to God" (De Augmentis Scientiarum III.4). The expulsion of teleology was one of the conditions for the birth of modern science.

2. The limits of logic: Aristotle's syllogistic handles only propositions of the subject–predicate form "A is B." But relational propositions such as "A is larger than B," or complex quantificational structures such as "For every x there exists a y such that…" lie beyond its reach. In the nineteenth century Frege inaugurated predicate logic and formalised these very types of inference. Aristotle's logic was a magnificent starting point that endured for two thousand years, but from the perspective of modern logic its scope is undeniably limited.

3. Natural slavery and views on women: Aristotle asserted that "some men are by nature slaves" (Politics I.5, 1254a14–17) and held that women are inferior to men in reason (I.13, 1260a12–14). While these positions reflect the social structures of antiquity, they are rightly criticised from the standpoint of modern egalitarianism. Any reception of Aristotle's thought must clearly acknowledge this limitation.

4. Reassessment by modern virtue ethics: In the second half of the twentieth century, prompted by Anscombe's essay "Modern Moral Philosophy" (1958), Aristotelian virtue ethics was revived as a third alternative to deontology and utilitarianism. MacIntyre's After Virtue (1981) and Nussbaum's The Fragility of Goodness (1986) are landmark works in this revival, contributing to the restoration of an ethics that asks "how should one live?"

Influence and Legacy

Islamic philosophy: In medieval Europe, many of Aristotle's works were no longer widely read directly in Greek or Latin, but they were preserved and transmitted through Arabic translation. Ibn Sīnā (Avicenna) and Ibn Rushd (Averroes) were renowned commentators on Aristotle; Averroes in particular was known in the West simply as "the Commentator."

Medieval Scholastic philosophy: When Aristotle's works were retranslated into Latin in the twelfth and thirteenth centuries, an intellectual revolution swept Europe. Thomas Aquinas attempted to synthesise Aristotelian philosophy with Christian theology, identifying the Unmoved Mover with the God of Christianity. Dante, in the Inferno, called Aristotle "the master of those who know" (il maestro di color che sanno) (Inferno IV.131).

The Scientific Revolution: The Scientific Revolution of the seventeenth century began as a revolt against Aristotle's natural philosophy. Galileo overturned Aristotle's theory of motion with his law of falling bodies, and Newton's mechanics replaced the teleological view of nature with mechanism. Yet, ironically, the very methodology of modern science — observation, classification, causal explanation — is deeply indebted to the framework Aristotle established.

Biology: On the island of Lesbos Aristotle observed and recorded over 500 species of animals, laying the foundations of taxonomy. Darwin wrote in a letter to William Ogle (1882): "Linnaeus and Cuvier have been my two gods, though in very different ways — but they were mere schoolboys to old Aristotle."

Connections to the Present

First, the revival of virtue ethics. Rather than asking "What should I do?" (deontology) or "How do I maximise outcomes?" (utilitarianism), Aristotelian ethics asks "What kind of person should I become?" This approach continues to be invoked in applied ethics today — in AI ethics, the ethics of care, and professional ethics.

Second, teleology and functionalism. It remains natural in biology to say "the heart exists in order to pump blood." Functional explanation is not strictly the same as Aristotle's final cause, but the two are structurally analogous. The relationship between teleological explanation and adaptation in evolutionary biology is still vigorously debated in the philosophy of science.

Third, the importance of practical wisdom (phronēsis). Aristotle distinguished theoretical knowledge (epistēmē) from practical wisdom (phronēsis). Practical wisdom is the capacity for judgement concerning "the good life" — a prudence that cannot be reduced to a manual and that responds to concrete circumstances. In an age when AI-driven decisions are proliferating, the concept of practical wisdom, which resists quantification, is arguably more important than ever.

Questions for the Reader

• Aristotle defines happiness (eudaimonia) as "activity of the soul in accordance with virtue." How does this stand in relation to modern hedonistic conceptions of well-being — the satisfaction of desires and subjective contentment? What does "the good life" mean to you?
• Aristotle's teleology was banished from natural science, yet in everyday life we constantly ask "What for?" Is teleological explanation truly dispensable, or is it indispensable to human understanding?
• Aristotle taught that virtue is acquired through habit. But in the environment of modern society — social media, consumer culture, information overload — how far is it possible to form "good habits"?

References

• (Primary source): Aristotle. The Complete Works of Aristotle: The Revised Oxford Translation. Ed. Jonathan Barnes. 2 vols. Princeton UP, 1984. — Standard English collected edition
• (Overview): Shields, Christopher. Aristotle. 2nd ed., Routledge, 2014. — Comprehensive introduction to Aristotle's philosophy
• (Study): Ross, W.D. Aristotle. 6th ed., Routledge, 1995. — Classic overview, still valuable
• (Study): Ackrill, J.L. Aristotle the Philosopher. Oxford UP, 1981. — A clear and accessible introduction
• (Ethics): MacIntyre, Alasdair. After Virtue. 3rd ed., Notre Dame UP, 2007. — A landmark of the modern revival of Aristotelian virtue ethics
• (Ethics): Nussbaum, Martha C. The Fragility of Goodness. Rev. ed., Cambridge UP, 2001. — Influential study of luck and ethics in Greek tragedy and philosophy
• (Web): Shields, Christopher. "Aristotle." Stanford Encyclopedia of Philosophy. https://plato.stanford.edu/entries/aristotle/