Bold hypothesis or bold conjecture is a concept in the philosophy of science of Karl Popper, 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). The concept is nowadays widely used in the philosophy of science and in the philosophy of knowledge. It is also used in the social and behavioural sciences.
Brief explanation
Popper's argument is that the growth of scientific knowledge progresses by means of formulating bold hypotheses, and trying to refute (disprove or falsify) them. Popper believed that:
He makes this point more specific in a 1953 lecture, where he argues that, if we aim to explain the world, then:
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 hypothesis depends mainly on:
Its scope – the number and variety of phenomena which it could explain, if it is true (its "explanatory power"). its novelty or originality – the extent to which the hypothesis is a genuinely new departure from the received scientific ideas. whether it enables new and novel predictions ("predictive power"). whether it stimulates new, innovative research ("heuristic power"). Its degree of applicability or usefulness for scientific research ("utility"). The effect or impact it has on existing scientific thinking, if it is true.
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, with the aim of finding counter-arguments which 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 generates new 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 theory which exists already. It can contribute rather little to advancing scientific progress, because it does not expand or add to scientific understanding very much.
According to Popper,
In Popper's philosophy of science, scientific statements are always provisional, they have limits of application, and they could always be wrong. If a statement cannot even in principle be proved wrong, it cannot be a scientific statement. Thus, in Popper's eyes, the falsifiability criterion clearly demarcates "science" from "non-science". This Popperian idea has been very controversial, however. The reason is that it can be quite difficult to test scientifically how true a particular idea is. Even if scientists do want to test an idea, they may not know yet how exactly to test it conclusively. Yet, scientists also don't want to abandon a hunch that seems useful, simply because they don't know how to verify it yet. This point is especially important for "bold" new hypotheses, because the very "boldness" of the new hypothesis could mean that it would take a lot of work before adequate tests could be designed.
Some philosophers have argued that, in the real world, scientists operate routinely with at least some metaphysical beliefs for which they have no proof or verification whatsoever. According to Paul Feyerabend, the creative processes that lead to a scientific discovery are usually quite reasonable and non-arbitrary. However, the creative processes are by no means fully "rational", and they can be quite unique. Thus, the idea that there is one standard model which can define the rationality of all scientific methods should be rejected.
In one of his later writings, Objective Knowledge (1972), Popper argued that:
This interpretation was criticized by Adolf Grünbaum.