---
title: "Bold hypothesis"
chunk: 1/4
source: "https://en.wikipedia.org/wiki/Bold_hypothesis"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T04:36:16.007133+00:00"
instance: "kb-cron"
---

Bold hypothesis (or bold conjecture, the terms are used interchangeably) is a concept originally created by the liberal philosopher Karl Popper when he tried to define the meaning of scientific thinking and scientific progress. It was first explained in his debut The Logic of Scientific Discovery (1935) and subsequently elaborated in writings such as Conjectures and Refutations: The Growth of Scientific Knowledge (1963), Objective knowledge: an evolutionary approach (1972), and Replies to my critics (1974). In successive texts written in the course of four decades, Popper added some nuances to the definition of the concept.
Broadly speaking, the idea of a bold hypothesis refers to a new, testable theoretical proposition (or theoretical claim) made within a subject area which, if it is true, would be able to explain and predict much more about the subject than was previously possible. It would significantly alter existing scientific understandings about the subject, in a positive way. The new idea would be very useful for scientific research about the subject. This contrasts with other types of scientific claims which, if they turn out to be true, make little difference to what scientists already know about the subject. The contrary of a bold hypothesis is an "ad hoc hypothesis" which protects a well-established scientific theory from refutation, by means of some convenient modification of this theory which has no new testable consequences. Alan F. Chalmers summarizes that, in Popper's philosophy of science,

"A very good theory will be one that makes very wideranging claims about the world, and which is consequently highly falsifiable, and is one that resists falsification whenever it is put to the test."
The idea of a "bold hypothesis" is nowadays widely used in the philosophy of science and in the philosophy of knowledge. It is also used in the social, historical and physical sciences, to refer to "significant new ways to understand something". Bold hypotheses are often understood to be an important ingredient of major scientific breakthroughs, scientific progress and scientific innovation. Bold hypotheses can help to move scientific understanding forward, by creating new concepts and formulations to understand something and testing them out. That is also why bold hypotheses have an important place in Karl Popper's theory of scientific progress. 
However, when bold hypotheses are formulated, they don't necessarily meet all the scientific criteria required to test them yet. And not all of them survive the scientific tests that are eventually done. Some hypotheses stand up to the evidence, while others do not. Testing a bold hypothesis conclusively can be difficult. It can sometimes take a long time, before a bold hypothesis is definitely accepted or rejected. There are also bold hypotheses which, although they were ultimately rejected after relevant tests, nevertheless triggered a lot of new and valuable ideas about what might (or might not) be the case. They might help to rule out a lot of possibilities, and focus the research with new leads. Sometimes it is helpful to know what cannot be true, in order to find out what is true.

== Brief explanation ==
Karl Popper's argument was that scientific progress occurs through formulating bold hypotheses, and trying to refute (disprove or falsify) them. Popper believed that:

"The advance of science is not due to the fact that more and more perceptual experiences accumulate in the course of time. Nor is it due to the fact that we are making ever better use of our senses. Out of uninterpreted sense-experiences science cannot be distilled, no matter how industriously we gather and sort them. Bold ideas, unjustified anticipations, and speculative thought, are our only means for interpreting nature: our only organon, our only instrument, for grasping her. And we must hazard them to win our prize. Those among us who are unwilling to expose their ideas to the hazard of refutation do not take part in the scientific game." 
He makes this point more specific in a 1953 lecture, where he argues that, if we aim to explain the world, then:

"... there is no more rational procedure than the method of trial and error – of conjecture and refutation: of boldly proposing theories; of trying our best to show that these are erroneous; and of accepting them tentatively if our critical efforts are unsuccessful. From the point of view here developed, all laws, all theories, remain essentially tentative, or conjectural, or hypothetical, even when we feel unable to doubt them any longer." 
In his 1974 reply to critics, Popper described the concept of bold hypotheses some more:  

“Bold ideas are new, daring, hypotheses or conjectures. And severe attempts at refutations are severe critical discussions and severe empirical tests. When is a conjecture daring and when is it not daring, in the sense here proposed? Answer: it is daring if and only if it takes a great risk of being false – if matters could be otherwise, and seem at the time to be otherwise.”
He added that the characteristic of bold conjectures, in combination with tests and refutations, is what distinguishes science from non-science, from prescientific myths and from metaphysics: