Knowledge and scepticism

Philosophers in many traditions have asked what we can know, how we come to know it, and whether doubt, once raised, can be answered. In India the theory of knowledge (pramāṇa-śāstra) became a genre of its own, spanning almost twenty centuries, in which schools debated which sources of knowledge, such as perception, inference and testimony, are genuine. Nāgārjuna asked what certifies those sources themselves; Nyāya philosophers replied that a doubter’s own actions contradict the doubt.

In China, Zhuangzi questioned whether any standpoint could be shown to be the right one, and later Confucians argued over whether moral knowledge comes from studying things or is already present in the mind. In the Islamic world, Suhrawardi set aside knowledge through mental representations in favour of the direct presence of what is known.

In Europe, Plato contrasted knowledge of unchanging forms with the error-filled world of the senses. Descartes made doubt a method for finding certain foundations, Hume argued that our expectations about the future rest on habit rather than reason, and Kant tried to show how some knowledge of the world can be certain after all.

Through time

4th century BCE

Plato

c. 429 – 347 BCE · Western

Plato held that the senses show a defective world full of error, so real knowledge is of the unchanging forms, which the soul grasps best when free of bodily distraction. In the Meno, learning is recollecting what the soul knew of the forms before birth.

Zhuangzi

fl. 350–300 BCE · Chinese

Zhuangzi doubted that any standpoint can be shown to be the right one: winning a dispute doesn’t make you correct, and no judge can settle it. His scepticism is modest rather than total, denying final certainty while allowing degrees of knowing, and it invites openness to other perspectives.

About 500 years later

2nd century CE

Nāgārjuna

fl. 150–250 CE · Indian

Nāgārjuna asked what certifies the sources of knowledge themselves: each needs a further warrant or must simply be declared self-validating. Sources and their objects establish each other, so neither has intrinsic nature, and he claimed to have no thesis of his own to defend.

About 400 years later

7th century CE

Dharmakīrti

c. 600 – c. 660 CE · Indian

Dharmakīrti recognised only two sources of knowledge: perception, which grasps real, momentary particulars without concepts, and inference, which works through concepts. A cognition counts as knowledge if it is reliable enough to act on, as when the vase we saw really does hold water.

About 600 years later

12th century

Suhrawardi

1154–1191 · Arabic and Islamic

Suhrawardi denied that we know things by acquiring forms or definitions of them in the mind, as the Peripatetic philosophers held. The most basic knowledge is the direct presence of a thing to the self, starting with the self’s awareness of itself, and only direct experience guarantees true knowledge.

Drew on Plato

14th century

Gaṅgeśa

fl. 1300–1350 · Indian

Gaṅgeśa, defending the Nyāya school, held that perception, inference, analogy and testimony, working properly, yield only true awareness. Doubt is answered by the doubter’s own conduct: no one can regularly turn to fire to get smoke while doubting that fire causes smoke.

16th century

Wang Yangming

1472–1529 · Chinese

Wang Yangming held that moral knowledge isn’t found by investigating external things, as Zhu Xi taught, but is the “pure knowing” already in every mind. Real knowing shows itself in action: those who know but do not act “simply do not yet know”.

17th century

René Descartes

1596–1650 · Western

Descartes set out to doubt everything that could be doubted, supposing he might be dreaming or misled by an evil deceiver. The certainty that he exists while thinking survived, and he argued that a God who is no deceiver guarantees whatever the intellect perceives clearly and distinctly.

18th century

David Hume

1711–1776 · Western

Hume argued that reason cannot justify our expectation that the future will resemble the past; such beliefs come from custom or habit. Yet total, Pyrrhonian doubt can’t be sustained, so he recommended a “mitigated” scepticism that lowers our confidence and limits the scope of our inquiries.

Immanuel Kant

1724–1804 · Western

Woken from his “dogmatic slumber” by Hume, Kant argued that we can know some things a priori, such as that every event has a cause, because the mind brings these forms to experience. Such knowledge is certain but reaches only as far as possible experience, never to things in themselves.

Drew on David Hume