Book: On Certainty

Overview
On Certainty gathers Ludwig Wittgenstein’s final notes (1950–51), published posthumously in 1969, into a sustained meditation on knowledge, doubt, and the conditions that make meaningful inquiry possible. Prompted by G. E. Moore’s attempts to refute skepticism by claiming to know obvious truths like “Here is a hand,” Wittgenstein examines how such claims function within language and life. He argues that epistemic concepts, know, doubt, justify, certain, operate within a framework of practices and assumptions that are neither discovered nor proved but taken for granted in action.

Context and Focus
The remarks circle around Moore’s “common sense” propositions and the skeptic’s challenges to them. Wittgenstein neither endorses Moore’s professed knowledge nor accepts the skeptic’s universal doubt. He recasts the debate by showing that both sides mislocate where certainty belongs. The result is not a theory of knowledge but a grammatical investigation: what we count as knowing and doubting depends on rules and roles within language-games anchored in a form of life.

Moore, Skepticism, and the Misuse of “Know”
Moore says he knows he has two hands and thereby claims to defeat the skeptic. Wittgenstein replies that the word “know” is out of place here. Knowledge normally presupposes possibilities of error, criteria of checking, and contexts in which doubt would make sense. With Moore’s examples, there is no live procedure of verification; the claim functions like a rule rather than a report. The skeptic’s global doubt fares no better, because doubt itself needs reasons and a background of undoubted practice. Where doubt lacks foothold, “I know” lacks sense; where doubt is intelligible, knowledge claims can be tested.

Hinge Propositions and World-Picture
Wittgenstein introduces what later readers call hinge propositions: statements like “The world has existed for many years” or “Objects persist when unobserved” that are not known by evidence yet stand fast and guide inquiry. They belong to a “world-picture,” a framework inculcated through training and shared practices. These certainties are not hypotheses competing with others; they are conditions for the comparison of hypotheses. They can be expressed as sentences, but their status is practical and grammatical, not evidential. They are arational in the sense that they neither need nor admit justification, and yet they are not arbitrary.

Language, Practice, and Bedrock
Certainty shows itself primarily in what we do. Teaching, measuring, remembering, trusting testimony, and using tools presuppose a bedrock of agreement. When justifications run out, what remains is the form of life: “This is simply what I do.” Wittgenstein’s riverbed image captures the stability and plasticity of the framework: most channels of thought flow within fixed beds, yet under pressure the bed itself may shift. Framework propositions can change, through scientific revolutions or cultural transformation, but not by the ordinary presentation of evidence within the very practices they underpin.

Knowledge, Doubt, and the Limits of Justification
Wittgenstein distinguishes knowledge from certainty without opposition. Knowledge claims are local, defeasible, and answerable to checks; certainty at the hinges is global, enacted, and groundless in the non-pejorative sense. Doubt requires sense and point; universal doubt voids the very criteria that would make it meaningful. The proper response to the skeptic is not to outbid with stronger knowledge but to reveal that epistemic terms only operate against a taken-for-granted background. Once this is seen, Moore’s “I know” becomes a rule-confession, while skeptical challenges dissolve as category mistakes.

Scope and Significance
On Certainty reframes epistemology through attention to grammar, practice, and the tacit background of inquiry. It displaces foundational proof with hinge certainty rooted in our communal ways of acting, showing that the possibility of error and the stability of certainty are interdependent features of our life with language.