Knowledge

Ancient Greek (Platonism)

Knowledge (epistēmē) must be sharply distinguished from mere belief (doxa): it is stable, gives an account of its reasons, and is directed at the eternal Forms rather than the shifting world of appearances. In the Theaetetus knowledge is examined as 'true belief with an account (logos),' the ancestor of the justified-true-belief analysis. Because we can recognize truths we were never taught, Plato suggests learning is really recollection (anamnesis) of what the soul once beheld.

Theaetetus; Meno; Republic (Divided Line, Books V–VII).

Ancient Greek (Peripatetic)

Scientific knowledge (epistēmē) is knowledge of universal and necessary truths through their causes: to know a thing is to grasp why it cannot be otherwise. Such knowledge is demonstrative, derived syllogistically from first principles that are themselves grasped by intuitive reason (nous) via induction from experience. Aristotle distinguishes this from craft (technē) and practical wisdom (phronēsis), each a distinct way the soul attains truth.

Posterior Analytics; Nicomachean Ethics, Book VI.

Islamic Aristotelianism

Human knowledge culminates when the individual intellect abstracts intelligible forms and receives them from the transcendent Active Intellect, which illuminates the mind as light illuminates the eye. His 'Floating Man' thought experiment — a person created suspended in the void, deprived of all sensation, who would still affirm his own existence — argues that self-awareness is immediate and independent of the body. Knowledge of essences is thus grounded in intellectual intuition, not sensation alone.

The Book of Healing (Kitāb al-Shifāʾ); the 'Floating Man' argument.

Islamic theology / Sufism

Seeking certainty, Al-Ghazālī undergoes a radical skeptical crisis, doubting even the senses and self-evident reason until he can trust nothing merely acquired by proof. He emerges not through new arguments but through a 'light which God cast into his breast' — the recovery of certainty by divine illumination and, ultimately, the direct experiential knowledge (dhawq, 'taste') of the Sufis. Demonstrative reason has its place, but the highest knowledge is a gift beyond it.

Deliverance from Error (al-Munqidh min al-Ḍalāl).

Rationalism

By methodical doubt Descartes seeks an unshakable foundation for knowledge and finds it in the cogito: even a deceiving demon cannot make me not exist while I think. From this first certainty, and clear and distinct ideas guaranteed by a non-deceiving God, he aims to rebuild the edifice of knowledge on reason rather than the untrustworthy senses. Genuine knowledge (scientia) is built deductively from indubitable first principles.

Meditations on First Philosophy (1641); Discourse on Method (1637).

British empiricism

The mind is at birth a blank tablet (tabula rasa); all our ideas derive ultimately from experience, whether outer sensation or inner reflection. There are no innate principles or ideas. Knowledge itself is 'the perception of the connexion and agreement, or disagreement and repugnancy' of our ideas, and it varies in degree from intuitive certainty to merely probable judgment.

An Essay Concerning Human Understanding (1689).

British empiricism

All contents of the mind are impressions and the fainter ideas copied from them, so any idea lacking such an origin is suspect. Reasoning divides into 'relations of ideas' (demonstrable but empty of fact) and 'matters of fact' (informative but never certain). Crucially, our belief in causation and induction cannot be rationally justified — it rests only on custom and habit, a skeptical result that shadows all empirical knowledge.

An Enquiry Concerning Human Understanding (1748).

Critical philosophy

Kant mediates rationalism and empiricism: 'thoughts without content are empty, intuitions without concepts are blind.' Knowledge requires that sensory intuitions be organized by the mind's a priori forms — space, time, and the categories — so that we know objects only as they appear, never things-in-themselves. This makes synthetic a priori knowledge possible (as in mathematics and pure physics) while confining knowledge to the bounds of possible experience.

Critique of Pure Reason (1781/1787).

Nyāya (Indian epistemology)

The founder of the Nyāya school offers a systematic theory of the 'means of valid knowledge' (pramāṇas), holding that there are four: perception, inference, comparison, and reliable testimony. Valid cognition (pramā) is that which apprehends its object as it really is, and liberation itself depends on correct knowledge of reality. Nyāya's careful analysis of inference and the conditions of error is one of the world's earliest developed epistemologies.

Nyāya Sūtras.

Philosophy of science

There is no inductive route to certain knowledge; we can never verify a universal theory, only falsify it. Scientific knowledge grows by bold conjectures that are exposed to severe attempts at refutation, and what marks a theory as scientific is precisely its falsifiability. All knowledge is thus conjectural and provisional — we do not possess truth but approach it through the elimination of error.

The Logic of Scientific Discovery (1934); Conjectures and Refutations (1963).

Philosophy of science

'We know more than we can tell': much of what we know is tacit, an inarticulate skill exercised in acts like riding a bicycle or recognizing a face. All knowing involves a personal, committed act of integration in which we attend from subsidiary clues to a focal whole, so the ideal of wholly impersonal, explicit knowledge is an illusion. Even science depends on the connoisseurship and judgment of the knower.

Personal Knowledge (1958); The Tacit Dimension (1966).

Analytic epistemology

In a three-page paper Gettier constructs cases in which a person has a justified true belief that nonetheless fails to be knowledge, because the justification is accidentally related to the truth. These counterexamples showed the classical 'justified true belief' analysis to be insufficient and launched decades of attempts to add a fourth condition or reconceive justification. The 'Gettier problem' reshaped modern epistemology overnight.

'Is Justified True Belief Knowledge?' (1963).

Post-structuralism

Foucault analyzes knowledge historically as bound up with power in the couplet 'power/knowledge': there is no knowledge that does not presuppose and constitute relations of power, and no power that does not produce a field of knowledge. Each era has an 'episteme' — a hidden order that defines what can be thought and what counts as a serious statement. Knowing is never a pure, disinterested mirroring of reality but is embedded in practices, institutions and discipline.

The Order of Things (1966); The Archaeology of Knowledge (1969).