Classical Western: Ancient, Medieval, and Modern

Overview

Three threads run through this whole unit, and naming them at the start of an answer will organise almost any question. The first thread is metaphysics: is reality one or many, material or ideal, changing or unchanging. The second is epistemology: does knowledge come from reason, from experience, or from a combination that must be explained. The third is the relation between philosophy and its neighbours: myth in the early period, faith in the medieval period, and natural science in the modern period. Notice how the same problem returns in new vocabulary. The Pre-Socratic search for an underlying stuff returns as substance in Descartes, Spinoza, and Leibniz. The Sophist challenge that truth is relative returns as Hume scepticism and as the problem of the external world. Plato division between Forms and sensible things returns as the distinction between primary and secondary qualities and as Kant distinction between phenomena and things in themselves. A good examination answer therefore does not merely list thinkers; it shows the problem each thinker inherits, the move that thinker makes, and the new problem that move creates. Keep chronology loose and argument tight: examiners reward a student who can say why Parmenides forced later thinkers to explain change, why Descartes needed God to guarantee clear ideas, and why Kant thought Hume had woken him from dogmatic slumber.

Pre-Socratics, Sophists, Socrates

Thales proposed water as the single source of all things, not because water is obviously everything but because a single material principle could explain diversity without appealing to separate gods for each phenomenon. Anaximander replaced water with the boundless, an indefinite stuff without determinate qualities, so that opposites like hot and cold could emerge from it without the source already being one of them. Anaximenes chose air, rarefied into fire and condensed into wind, cloud, water, and earth, giving a mechanism of change through density. Heraclitus made change itself the principle: all things flow, you cannot step into the same river twice, and the logos is the hidden order governing the flux, so stability is an illusion produced by a balanced strife of opposites. Parmenides argued the opposite with ruthless logic: what is, is, and cannot come from what is not, so change, plurality, and empty space are impossible, and reality is one, ungenerated, indivisible, and unchanging. The clash between Heraclitus and Parmenides set the agenda: any later theory had to save both the appearance of change and the logical demand for a stable reality. Empedocles answered with four roots mixed by love and strife, Anaxagoras with infinitely many seeds ordered by mind, and the atomists Leucippus and Democritus with indivisible atoms moving in the void, so that change is rearrangement of unchanging parts rather than creation or destruction. Pythagoras added number as the key to reality, seeing mathematical ratios in music and in the cosmos. The Sophists shifted attention from nature to human life: Protagoras declared that man is the measure of all things, making truth relative to the perceiver, and Gorgias argued that nothing exists, that if it did it could not be known, and that if known it could not be communicated. They taught rhetoric for success in democratic Athens, and their relativism challenged any claim to objective knowledge or morality. Socrates answered not with a rival system but with a method. He claimed to know only that he did not know, and he cross-examined confident speakers until their definitions collapsed, showing that they did not know what they claimed to know. This elenchus was not mere cleverness: Socrates believed that virtue is knowledge, that no one does wrong knowingly, and that the soul must be cared for more than wealth or reputation. His trial and death made the point dramatically: he refused to abandon philosophy even at the cost of his life, because a life without examination was not worth living. The difference from the Sophists is crucial: Sophists taught how to win arguments for pay, while Socrates sought definitions that would hold for everyone, and that search for universal definitions became Plato project.

Plato and Aristotle

Plato theory of Forms claims that the objects of the senses are imperfect copies of eternal, non-physical realities. A beautiful thing is beautiful because it participates in the Form of Beauty, a just act because it participates in Justice, and a circle drawn in sand because it approximates the Form of Circle. The Forms are known by reason, not by the senses, and the soul before birth knew them directly, so learning is recollection of what the soul already knows. The divided line grades cognition from imagination and belief about sensible things to thought and understanding of Forms, and the cave allegory pictures prisoners mistaking shadows for reality until one escapes, sees the sun, and returns to free the others, at the cost of ridicule. Plato psychology divides the soul into reason, spirit, and appetite, and his political theory makes the city the soul writ large: philosopher-kings ruled by reason, guardians animated by spirit, and producers driven by appetite, with justice as each part doing its own work without interfering. Aristotle, Plato pupil, rejected separate Forms and located form within things: every substance is a compound of matter, the stuff it is made of, and form, the organisation that makes it what it is. He analysed causation into four causes: material, formal, efficient, and final, so that a statue is explained by its bronze, its shape, its sculptor, and its purpose. His logic invented the syllogism, the study of categories, and the laws of non-contradiction and excluded middle, and his physics treated nature as purposive, with each thing striving toward its natural place and end. In ethics Aristotle argued that the good for humans is activity of soul in accordance with virtue over a lifetime, and virtue is a mean between excess and deficiency determined by practical wisdom, not by a formula. Courage lies between cowardice and rashness, generosity between stinginess and wastefulness, and the mean is relative to us, found by the person of practical wisdom. His politics defended the polis as natural, classified constitutions by who rules and whether they rule for the common good, and warned that the middle class stabilises a city. The contrast to hold is sharp: Plato separates the real from the sensible and trusts reason to ascend, while Aristotle keeps form inside the world and trusts observation disciplined by logic, which is why later philosophy oscillates between Platonism and Aristotelianism.

Medieval philosophy

Medieval philosophy is the attempt to think faith with reason, in Christian, Jewish, and Islamic traditions, without reducing one to the other. Augustine, drawing on Plato, argued that truth is illuminated by God as the sun illuminates visible things, that evil is not a substance but a privation of good, and that human freedom is compatible with divine foreknowledge because God sees all time at once rather than causing every choice. Anselm offered the ontological argument: God is that than which nothing greater can be conceived, and a God who exists in reality is greater than one who exists in thought alone, so God must exist in reality. Gaunilo replied with the perfect island: the same reasoning would prove a perfect island, which is absurd, so existence is not a property that can be added to a concept. Aquinas, drawing on Aristotle, rejected the ontological argument and offered five ways, each starting from experience: motion requires a first mover, efficient causes require a first cause, contingent things require a necessary being, degrees of perfection require a maximum, and the ordered direction of natural things requires an intelligence directing them. His synthesis holds that reason can prove that God exists and some attributes of God, while truths like the Trinity require revelation, so faith and reason are distinct but never contradictory. The problem of universals asked whether general terms like humanity name real things or mere words. Realists held that universals exist, either separately as in Plato or in things as in Aristotle; conceptualists held that they exist as concepts in the mind; nominalists, most sharply William of Ockham, held that only individuals exist and universals are names, with Ockham razor cutting away entities that are not needed. Ockham razor, that entities should not be multiplied beyond necessity, became a permanent methodological principle. Islamic and Jewish thinkers were essential to this story: Avicenna distinguished essence from existence and argued for a necessary being whose essence is existence itself, Averroes defended philosophy against theology and influenced Latin debates about the unity of intellect, and Maimonides argued that scriptural language about God must be read negatively, since positive attributes would limit the unlimited. Medieval philosophy therefore is not a pause between ancient and modern thought; it is where logic, metaphysics, and theology were fused into systems that modern thinkers had to dismantle or inherit.

Descartes, Spinoza, Leibniz

Modern rationalism begins with Descartes method of doubt. He resolves to reject anything that can be doubted, including the senses, which deceive, dreams, which mimic waking life, and even mathematics, which an evil demon might falsify. What survives is the cogito: I think, therefore I am, because doubting itself proves a doubter. From the idea of a perfect God he argues that God must exist, since existence belongs to perfection, and from a non-deceiving God he recovers the external world and the reliability of clear and distinct ideas. Descartes substance dualism divides reality into thinking substance, whose essence is thought, and extended substance, whose essence is extension, with the human being as their union, a union he could never satisfactorily explain, since interaction between an unextended mind and an extended body remains mysterious. Spinoza removed the mystery by removing the duality: there is only one substance, God or Nature, with infinite attributes, of which thought and extension are the two known to us. Everything else is a mode of that substance, so mind and body are not two things interacting but one thing conceived under two attributes, like two descriptions of the same event. Freedom in Spinoza is not uncaused choice but understanding necessity: a person is free when acting from the necessity of their own nature rather than being driven by external passions, and the intellectual love of God is the highest blessedness. Leibniz kept plurality but made it harmonious: reality consists of infinitely many monads, simple windowless substances that mirror the universe from their own point of view, each unfolding according to its own internal principle. Monads do not causally interact; God established a pre-established harmony so that the perceptions of one monad correspond to the perceptions of others, as two perfectly synchronised clocks. This is the best of all possible worlds, Leibniz argued, because God chose the world with the greatest variety compatible with the greatest order, and apparent evils are necessary parts of that optimum. The three rationalists thus offer three answers to one question, how many substances are there: Descartes says two, Spinoza says one, Leibniz says infinitely many, and each answer carries a different account of mind, body, freedom, and God.

Locke, Berkeley, Hume, Kant, Hegel

Locke empiricism starts from the opposite pole: the mind is a blank slate and all ideas come from sensation or reflection on the mind operations. Simple ideas are passively received, complex ideas are built by combining, comparing, and abstracting, and knowledge is the perception of agreement or disagreement between ideas. He distinguishes primary qualities, like solidity, extension, figure, and motion, which really are in objects, from secondary qualities, like colour, taste, and sound, which are powers in objects to produce sensations in us. He defends tolerance and government by consent, arguing that political power is a trust that may be resisted when it breaks its trust. Berkeley attacked the distinction itself: to be is to be perceived, and there is no matter behind our ideas, because the very idea of matter existing unperceived is unintelligible. The table exists when perceived by a mind, and its continued existence when no finite mind perceives it is secured by God perceiving all things. Berkeley is therefore an immaterialist, not a sceptic: the world is real, but it is a world of ideas sustained by minds, not of material substance. Hume pushed empiricism to its sceptical conclusion. All perceptions divide into impressions, lively and forceful, and ideas, faint copies of impressions, and any idea without a corresponding impression is suspect. Causation is not observed: we see one event follow another, never a necessary connection, so causal belief is a habit of the mind formed by constant conjunction, not rational insight. The self fares no better: looking inward Hume finds only a bundle of perceptions, never a self that owns them, so personal identity is a fiction of memory and imagination. His problem of induction states that no number of observed instances can logically guarantee the next, since the future resembling the past is itself an assumption that cannot be proved without circularity. Kant answered Hume by changing the question. He asked not whether knowledge matches things in themselves but what makes experience possible at all. Space and time are forms of intuition, categories like substance and causation are concepts of the understanding, and together they structure every possible experience, so synthetic a priori judgments are possible: judgments that add to knowledge yet are known independently of experience, as in mathematics and in the principles of natural science. We know phenomena, things as they appear under these forms, and not noumena, things as they are in themselves, which limits knowledge in order to make room for faith and morality. In morality Kant grounds duty in the categorical imperative: act only on a maxim you can will as universal law, treat humanity always as an end and never merely as a means, and act as a member of a kingdom of ends. Hegel historicised reason itself: reality is spirit realising itself through dialectic, in which a thesis generates its antithesis and both are preserved and overcome in a synthesis. History is not a random sequence but the progress of freedom becoming conscious of itself, from oriental despotism through Greek and Roman forms to the modern state, and philosophy is its own time comprehended in thought, arriving after the fact like the owl of Minerva flying at dusk.

Three rationalist answers to how many substances exist

Empiricist progression