---
title: "Bold hypothesis"
chunk: 2/4
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"
---

”There is a reality behind the world as it appears to us, possibly a many-layered reality, of which the appearances are the outermost layers. What the great scientist does is boldly to guess, daringly to conjecture, what these inner realities are like. (…) The boldness can be gauged by the distance between the world of appearance and the conjectured reality, the explanatory hypotheses. But there is another, a special kind of boldness – the boldness of predicting aspects of the world of appearance which so far have been overlooked but which it must possess if the conjectured reality is (more or less) right, if the explanatory hypotheses are (approximately) true. It is this more special kind of boldness which I have usually in mind when I speak of bold scientific conjectures. It is the boldness of a conjecture which takes a real risk – the risk of being tested and refuted; the risk of clashing with reality. Thus my proposal was, and is, that it is this second boldness, together with the readiness to look out for tests and refutations, which distinguishes “empirical” science from nonscience, and especially from prescientific myths and metaphysics.” 
This passage makes it very clear, that the idea of bold hypotheses also has a central role in Popper's solution for the demarcation problem, i.e. the problem of how scientific knowledge and scientific practice can be distinguished from non-scientific beliefs and practices.

=== Defining the boldness of hypotheses ===
A "bold" hypothesis is a new scientific idea which, if it was true, would be able to predict and/or explain a lot, or a lot more, about the subject  being theorized about.  The "boldness" of a scientific hypothesis can be evaluated with the following criteria:

Testability: the degree to which the hypothesis can be comprehensively tested (or, the extent to which the hypothesis can be definitely proved right or wrong, with available scientific methods).
Risk: the likelihood that the hypothesis which is to be tested will turn out to be wrong when tests are carried out.
Novelty: the extent to which the hypothesis represents a genuinely new departure from what scientists already know from established scientific ideas (or compared to background knowledge).
Heuristic power: whether the hypothesis stimulates new, innovative research that goes beyond the conventional or established approaches.
Predictive power: whether the hypothesis enables genuinely new and better predictions involving new phenomena (or forecasts which are not trivial), if the hypothesis is true.
Scientific impact: whether the hypothesis would have a major impact on existing scientific thinking, if it is true (or, how much it could change scientific thinking or scientific theory).
Explanatory power/depth: the scope or reach of the hypothesis – the size, number and variety of phenomena which it would explain, if it is true.

=== Testing hypotheses ===
Once a bold hypothesis has been mooted, Popper argues, scientists try to investigate and test how well the bold hypothesis can stand up to the known evidence. They try to find counter-arguments that would refute or falsify the bold hypothesis. In this process of testing and criticism, new scientific knowledge is generated. Even if the bold hypothesis turns out to have been wrong, testing it may well generate useful knowledge about what can and cannot be the case. Often it stimulates new research.
Inversely, if a hypothesis lacks the quality of boldness, then it would make very little difference to what scientists already know. It is not "a big deal", i.e. it is not very significant for the knowledge which exists already. It contributes little to advancing scientific progress, because it does not expand or add anything much to scientific understanding.

=== Tentative knowledge ===
According to Popper,

"Science does not rest upon solid bedrock. The bold structure of its theories rises, as it were, above a swamp. It is like a building erected on piles. The piles are driven down from above into the swamp, but not down to any natural or ‘given’ base; and if we stop driving the piles deeper, it is not because we have reached firm ground. We simply stop when we are satisfied that the piles are firm enough to carry the structure, at least for the time being." " 
In one of his later writings, Objective Knowledge (1972), Popper argued that:

"A theory is the bolder the greater its content. It is also the riskier: it is the more probable to start with that it will be false. We try to find its weak points, to refute it. If we fail to refute it, or if the refutations we find are at the same time also refutations of the weaker theory which was its predecessor, then we have reason to suspect, or to conjecture, that the stronger theory has no greater falsity content than its weaker predecessor, and, therefore, that it has the greater degree of verisimilitude". 
This interpretation was criticized by Adolf Grünbaum.

== Main criticisms ==
Popper's idea of the role of bold hypotheses in scientific progress has attracted four main kinds of criticisms. These concern (1) the meaning of "boldness", (2) the issue of testability, (3) the issue of falsifiability, and (4) the realities of normal science.

=== Boldness issue ===
The idea of a bold hypothesis is itself somewhat fuzzy, because exactly "how bold is bold" in scientific boldness? 