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Every thinker on the site in one table: where knowledge comes from, what justification does, whether knowledge can grow without limit, and what knowledge is physically.

Lifespans, each linked to its page. Filled bars: knowledge needs no justification. Open bars: it must be justified. Tinted bars: a qualified answer. Sextus Empiricus, whose dates are uncertain, and Chiara Marletto and Brett Hall, who are living, are in the table but not on the chart.

The four questions asked on every thinker page. Deutsch's answers stay in view for reference.
Thinker	Where does knowledge come from?	What does justification do?	Can knowledge grow without limit?	What is knowledge, physically?
Deutsch	Conjecture: guesses, improved by criticism and experiment.	No justificationNothing. No theory is ever justified, and none needs to be.	Without limitYes. Problems are inevitable, and problems are soluble.	Information that, once embodied, tends to keep itself in existence.
Xenophanes	Searching and guessing. Nothing was revealed.	No justificationNone is to be had. Even a true statement could not be known to be true.	Without limitYes, in effect. By searching, people find better as time goes on.	No account.
Socrates and Plato	Recollection of what the soul already knows, drawn out by questioning.	Needs justifyingIt turns true belief into knowledge, by tying it down with an account.	QualifiedUp to a ceiling. The Forms are fixed, and to know them is to be finished.	Nothing physical. A state of an immaterial soul in touch with the Forms.
Aristotle	Perception, memory and experience, from which the mind grasps first principles.	Needs justifyingEverything. Knowledge is demonstration from principles that are certain.	LimitedNo. A finished science is a complete chain of demonstrations.	A state of the soul, which takes on the form of the thing known without its matter.
Sextus Empiricus	Nowhere that can be shown. Every proposed source is disputed.	QualifiedEverything would depend on it, and it always fails: regress, circle or bare assumption.	LimitedNo. Inquiry continues, but it ends each time in suspended judgement.	No view. He suspends judgement.
Francis Bacon	Observation and experiment, sifted by a fixed method.	Needs justifyingCareful induction licenses each step up from particulars to laws.	Without limitYes. Knowledge will increase, and human power with it.	No account. A true image of nature in a mind cleansed of its idols.
René Descartes	Reason. Clear and distinct ideas, some of them innate.	Needs justifyingEverything must rest on a foundation that cannot be doubted, guaranteed by God.	QualifiedAs far as a finite mind can reach by deduction from the foundation.	Nothing physical. Thought belongs to an immaterial mind.
John Locke	Experience alone: sensation, and reflection on the mind's own workings.	Needs justifyingBelief should be proportioned to the evidence that experience supplies.	LimitedNo. Our ideas set a narrow limit, and beyond it there is only probability.	Ideas in the mind, produced by the action of bodies on the senses.
David Hume	Experience, extended beyond itself by custom.	QualifiedIt is required and cannot be had. Induction rests on habit, not reason.	LimitedNo. Reason cannot carry us beyond what experience has shown.	Impressions, and the fainter ideas copied from them, linked by association.
Immanuel Kant	Experience supplies the matter; the mind supplies the form.	Needs justifyingThe mind's categories are proved necessary for any experience at all.	LimitedNo. Things as they are in themselves lie beyond all possible knowledge.	No physical account. The knowing subject stands outside the nature it orders.
Karl Popper	Conjecture, tested by attempts at refutation.	No justificationNothing. Theories can be corroborated by surviving tests, never justified.	Without limitYes. Every solution opens new problems, without end.	Objective content in a "World 3" of theories and arguments: real, but not physical.
Michael Polanyi	Skilled, largely tacit acts of knowing, learned inside a tradition.	QualifiedPersonal commitment and the judgement of a community stand where proof was meant to be.	Without limitYes, wherever science is left free to govern itself.	Embodied skill. It lives in trained people more than in texts.
W. V. O. Quine	Sensory stimulation, organised by the whole web of theory.	QualifiedBeliefs are supported together, never one by one, and chosen for simplicity and fit.	QualifiedThe web can always be revised, but its only evidence is what reaches the senses.	Dispositions of a nervous system to respond to stimulation.
Edmund Gettier	Not addressed. His question is what knowledge is, not where it comes from.	Needs justifyingIt is necessary for knowledge, and his cases show it is not sufficient.	QualifiedNot addressed.	A state of a believer: a belief that is true and suitably justified.
Thomas Kuhn	Puzzle-solving inside a paradigm that a community shares.	QualifiedStandards of justification belong to a paradigm and change when it does.	QualifiedScience gets better at solving puzzles, but does not draw closer to the truth.	A social possession: the shared practice of a scientific community.
Imre Lakatos	Research programmes that predict novel facts.	QualifiedA programme earns its standing by progress over time, never by proof.	Without limitYes, for as long as programmes remain progressive.	Objective content, as for Popper: a "World 3" of theories and problems.
Paul Feyerabend	Anywhere: myth, metaphysics, rival traditions, deliberate rule-breaking.	No justificationNothing. Standards of justification are local to a tradition.	QualifiedNo measure of growth is common to all traditions.	The practice of a tradition, with no privileged form.
Donald Campbell	Blind variation and selective retention, at every level from genes to science.	No justificationNothing. What has survived selection has not been proved.	Without limitYes, in principle. Selection never has to stop.	A fit between a system and its environment, stored in genes, brains and cultures.
The Bayesians	Evidence, which shifts degrees of belief.	Needs justifyingA degree of belief is justified when it has been updated correctly by Bayes' theorem.	QualifiedCredences can sharpen for ever, but only among hypotheses already thought of.	Degrees of belief in an agent: in practice, weights in a brain or a machine.
Chiara Marletto	Conjecture and criticism in minds; variation and selection in genes.	No justificationNothing. The same answer as Deutsch.	Without limitYes. Whatever the laws of physics do not forbid, knowledge can bring about.	Resilient information: it can act as a constructor and so remain embodied.
Brett Hall	Conjecture and criticism. The same answer as Deutsch.	No justificationNothing. He treats the demand for justification as the root error of most epistemology.	Without limitYes. He defends Deutsch's optimism against its critics.	As Deutsch and Marletto define it: information that tends to stay embodied.