Kant's major critical works contain no sustained treatment of testimony (belief formed on the basis of others' assertions), yet his scattered remarks — the footnote to the 1786 orientation essay in which someone who has never been to Rome can be said to know that Rome exists on the basis of reports, the taxonomy of opinion, belief, and knowledge in the published logic, and the transcripts of his logic lectures with their 'Rule of Fairness' — have been read, most systematically by Joseph Shieber (2010), as composing an anti-reductionist theory of testimonial entitlement: merely understanding another's assertion gives a hearer prima facie warrant to believe it, absent defeaters, without independent corroboration. Whether that reconstruction is stable remains open. Four linked questions are unresolved: (1) whether Kant's remarks unify into a consistently anti-reductionist theory, or whether the same materials, which also demand open-eyed examination of witnesses, support only a mixed position on which testimony is basic for ordinary empirical beliefs while requiring checking in some contexts; (2) how far the default entitlement extends, given Kant's restriction of testimonial knowledge to empirical propositions and his denial that mathematical, philosophical, or moral truths can be known (or, for the latter two, even believed) on testimony; (3) whether the truth-directed norm of communication that grounds the entitlement can be reconciled with strategic and social uses of language without being weakened into vacuity; and (4) what evidential authority Kant's student-transcribed lecture materials carry for the reconstruction at all. Later literature (Newton 2014; Lu-Adler 2022; Gelfert 2024) has extended parts of the reconstruction — on communicability, on the historical/rational cognition boundary, on scientific communication — without settling any of these questions.

Background

In contemporary epistemology, 'testimony' names the epistemic source constituted by others' assertions: much of what anyone knows about history, distant places, and science is believed on the say-so of others. The central normative question is whether such belief needs independent justification. Reductionists hold that a hearer is warranted in accepting testimony only if she has positive non-testimonial evidence (inductive or perceptual) that the speaker is reliable; anti-reductionists hold that testimony is a basic source of warrant, so that a hearer who understands an assertion has a default, defeasible entitlement to accept it unless she has specific reasons to doubt it. An 'entitlement' here is prima facie warrant that need not be earned by antecedent evidence, and 'defeaters' are reasons to doubt that would remove it.

Kant's position in this debate is puzzling. The Critiques contain no theory of testimony, and Kant's ideal of enlightenment — thinking for oneself rather than deferring to others — suggests an epistemological individualism. Yet scattered texts point another way. In a footnote to the 1786 essay 'What does it mean to orient oneself in thinking?', Kant observes that someone who has never been to Rome can know (not merely believe) that Rome exists on the basis of trustworthy reports. The logic compiled by Gottlob Benjamin Jäsche from Kant's lectures (1800) works with a taxonomy of assent deriving from Kant's textbook author Georg Friedrich Meier — opinion (subjectively and objectively insufficient), belief or Glaube (subjectively sufficient only), and knowledge (both sufficient) — and Meier had defined historical belief (fides historica) as assent grounded in a credible witness's testimony (as documented in Mileti Nardo 2025). In the same logic materials, Kant restricts testimonial knowledge to empirical propositions: mathematical truths may be believed but not known on testimony, while philosophical and moral truths are not even properly believable on it. The student transcripts of Kant's logic lectures (the Vorlesungen, cited by Academy edition, 'AA', volume:page — the standard scholarly edition of Kant's collected works) list criteria of witness reliability (competence, integrity, reflectiveness, reliable memory, clear expression) and distinguish eyewitnesses from mere transmitters of hearsay; they also contain both a 'Rule of Fairness' — hold people honest until the contrary is shown — and an immediately adjacent demand that right knowledge requires examining whether a speaker speaks truly. In the Doctrine of Virtue §9 of the Metaphysics of Morals, Kant condemns lying as a subversion of the communicative function of language, since language exists for the communication of thought.

Oliver Robert Scholz (2001) and, most influentially in English, Axel Gelfert (2006) assembled this textual basis and read Kant as a proto-anti-reductionist; Kjartan Koch Mikalsen (2010) connected testimony to Kant's idea of public reason. Joseph Shieber (2010) then argued for the most systematic anti-reductionist reconstruction: the entitlement to believe what one understands another asserting is grounded in the normative structure of rational agency — a norm of belief on which one should believe only what one's evidence could underwrite as knowledge, so that a rational speaker asserts only what she knows — and in the truth-directedness of linguistic communication, inferable from the wrongness of lying. He answered the objection from strategic uses of language (jokes, irony, storytelling) by arguing that such nonliteral uses succeed only against a background of truth-directed assertion, and the objection from the social functions of language (coordination, gossip) by arguing that these presuppose broadly accurate communication. What Shieber's reconstruction leaves open — and what later work has not settled — is whether the overall reading is stable: whether the presumption-of-honesty and check-your-witness strands of the lecture materials can be held together by one principled theory, how far the entitlement extends beyond empirical propositions, whether the underlying norm of communication survives the full range of strategic and social uses of language, and how much evidential weight the student-transcribed lecture materials can bear at all.

Problem Statement

Decide whether Kant's scattered remarks on testimony can be systematically unified into a stable, consistently anti-reductionist theory of testimonial entitlement — a theory on which a hearer's understanding of another's assertion is itself a basic, defeasible source of warrant for believing it, requiring no positive non-testimonial corroboration — or whether Kant's texts and wider system support instead a mixed position, on which testimony is basic for ordinary empirical beliefs but still requires checking in some contexts, or whether the textual record sustains neither. The question turns on four stress points:

(1) Unification versus mixture. Adjudicate the tension internal to the lecture materials between the Rule of Fairness (hold speakers honest until the contrary is shown) and the adjacent demand that right knowledge requires examining whether a speaker speaks truly, by giving a principled account of the entitlement's default-and-defeater structure within Kant's system, or by showing that no such account is available and that the texts support only the mixed reading, or by showing that the texts sustain neither the anti-reductionist nor the mixed reading.

(2) Scope. Fix how far the default entitlement extends across Kant's taxonomy of cognition — empirical (historical) propositions versus mathematical, philosophical, and moral truths, which Kant denies can be known on testimony (and, for the latter two, even believed) — and either ground the resulting boundary in Kant's distinction between historical and rational cognition or show that the anti-reductionist entitlement cannot be bounded in the way the reconstruction requires.

(3) Normative basis. Determine whether the truth-directed norm of communication from which the entitlement is derived — via the condemnation of lying as a subversion of language's communicative function and the norm of belief linking rational assertion to knowledge — can be maintained against the existence of strategic and social uses of language (nonliteral uses such as jokes, irony, and storytelling, and social functions such as coordination and gossip) without being weakened into vacuity.

(4) Evidential basis. Take and defend an explicit methodological stance on the authority of the student-transcribed lecture materials (the Vorlesungen) relative to the published corpus, on which the reconstruction principally depends.

The question's resolution boundary is a defended overall verdict — a stable anti-reductionist theory, a mixed position, or the conclusion that the textual record sustains neither.

References

  1. Joseph Shieber, 'Between Autonomy and Authority: Kant on the Epistemic Status of Testimony', Philosophy and Phenomenological Research 80(2), 2010, pp. 327-348. DOI: 10.1111/j.1933-1592.2010.00329.x, https://doi.org/10.1111/j.1933-1592.2010.00329.x
  2. Oliver Robert Scholz, 'Autonomie angesichts epistemischer Abhängigkeit. Kant über das Zeugnis anderer', in Kant und die Berliner Aufklärung, 2001, pp. 829-839. DOI: 10.1515/9783110874129.1199, https://doi.org/10.1515/9783110874129.1199
  3. Axel Gelfert, 'Kant on Testimony', British Journal for the History of Philosophy 14(4), 2006, pp. 627-652. DOI: 10.1080/09608780600965226, https://doi.org/10.1080/09608780600965226
  4. Kjartan Koch Mikalsen, 'Testimony and Kant's Idea of Public Reason', Res Publica 16(1), 2010, pp. 23-40. DOI: 10.1007/s11158-009-9105-3, https://doi.org/10.1007/s11158-009-9105-3
  5. Joseph Shieber, 'Against Credibility', Australasian Journal of Philosophy 90(1), 2012, pp. 1-18. DOI: 10.1080/00048402.2011.560953, https://doi.org/10.1080/00048402.2011.560953
  6. Alexandra Newton, 'Kant on Testimony and the Communicability of Empirical Knowledge', Philosophical Topics 42(1) (issue 'The Second Person'), 2014, pp. 271-290. DOI: 10.5840/philtopics201442112, https://doi.org/10.5840/philtopics201442112
  7. Kristoffer Ahlstrom-Vij, 'Is There a Problem With Cognitive Outsourcing?', Philosophical Issues 26(1), 2016, pp. 7-24. DOI: 10.1111/phis.12072, https://doi.org/10.1111/phis.12072
  8. Joseph Shieber, 'Socially Distributed Cognition and the Epistemology of Testimony', in The Routledge Handbook of Social Epistemology, Routledge, 2019, pp. 87-95. DOI: 10.4324/9781315717937-9, https://doi.org/10.4324/9781315717937-9
  9. Sofie Møller, Kant's Tribunal of Reason: Legal Metaphor and Normativity in the Critique of Pure Reason, Cambridge University Press, 2020. DOI: 10.1017/9781108682480, https://doi.org/10.1017/9781108682480
  10. Martin Sticker, 'Kant on thinking for oneself and with others — the ethical a priori, openness and diversity', Journal of Philosophy of Education 55(6), 2021, pp. 949-965. DOI: 10.1111/1467-9752.12615, https://doi.org/10.1111/1467-9752.12615
  11. Huaping Lu-Adler, 'Kant's use of travel reports in theorizing about race — A case study of how testimony features in natural philosophy', Studies in History and Philosophy of Science 91, 2022, pp. 10-19. DOI: 10.1016/j.shpsa.2021.10.020, https://doi.org/10.1016/j.shpsa.2021.10.020
  12. Axel Gelfert, 'Kant on scientific pedantry and epistemic populism', Inquiry, published online 10 June 2024, pp. 1-20. DOI: 10.1080/0020174X.2024.2364733, https://doi.org/10.1080/0020174X.2024.2364733
  13. Ori Freiman, 'AI-Testimony, Conversational AIs and Our Anthropocentric Theory of Testimony', Social Epistemology 38(4), 2024, pp. 476-490. DOI: 10.1080/02691728.2024.2316622, https://doi.org/10.1080/02691728.2024.2316622
  14. Axel Gelfert, 'The Epistemology of Testimony', in The Oxford Handbook of Social Epistemology, Oxford University Press, 2025, pp. 22-38. DOI: 10.1093/oxfordhb/9780190949945.013.2, https://doi.org/10.1093/oxfordhb/9780190949945.013.2
  15. Lorenzo Mileti Nardo, 'Kant on the Feeling of Certainty', Con-Textos Kantianos: International Journal of Philosophy 21, 2025, pp. 51-63. DOI: 10.5209/kant.101667, https://doi.org/10.5209/kant.101667
  16. Adam Cureton, Sovereign Reason: Autonomy and our Interests of Reason, Oxford University Press, 2025. DOI: 10.1093/9780191960253.001.0001, https://doi.org/10.1093/9780191960253.001.0001
  17. Laurenz Ramsauer, 'Kant's Dialectic of Enlightenment', European Journal of Philosophy 34(2), 2026 (online 2025), pp. 639-655. DOI: 10.1111/ejop.70056, https://doi.org/10.1111/ejop.70056
  18. Thomas Grundmann, Expert Authority and the Limits of Critical Thinking, Oxford University Press, 2026. DOI: 10.1093/9780198971016.001.0001, https://doi.org/10.1093/9780198971016.001.0001
  19. Weng Hong Yue, 'How is "AI testimony" possible? A "Non-Anthropocentric" Attempt to Defend "Technological Testimony"', Dia-noesis: A Journal of Philosophy 19(1), 2026, pp. 321-344. DOI: 10.12681/dia.45790, https://doi.org/10.12681/dia.45790