Rejecting Certainty: Karl Popper's contribution to the modern scientific method

Long before the work of Karl Popper, the traditional scientific method relied on the doctrine of observational induction. That is, scientific theories can in some way be ‘validated’ through experimental observation, which can then be used to support some previously formed hypothesis. This can be regarded as an approach of ‘positive verification’, wherein theories are said to be true with enough experimental backing. Although at first glance this may seem to resemble the modern scientific method, the writings of Karl Popper have significantly altered the way in which the scientific community associates experimental evidence with hypotheses.

At the foundation of his work, Popper entirely rejected observational induction as a pathway to certainty. Popper believed observational induction to be a doctrine which was far too inconsistent to play a role in the natural sciences. Alternatively, Popper advocated for methods of empirical ‘falsification’, wherein scientific theories and hypotheses could only be proven to be false, rather than in any way ‘verified’ by experimental evidence. ‘Falsification’ arises when enough significant experimental data is found to confidently reject some hypothesis, thereby proving the theory from which the conclusion was deduced to be false. 

Popper’s primary reason for rejecting observational induction was its reliance on the idea that singular observations can somehow be viewed to be universal. In Popper’s own words, “people who say of a universal statement that we know its truth from experience usually mean that the truth of this universal statement can somehow be reduced to the truth of singular one”. Popper argued that no scientific rule can ever absolutely be certified from a scientific observation. Regardless of the number of times the experiment is repeated with supporting data, the supported theory can never become a scientific truth.

(Note: Popper’s claim that induction only provides ‘probable assumption’ rather certain truths has notable parallels with philosopher David Hume’s argument from induction that “it is impossible to justify a law by observation or experiment, since it transcends experiment”.)

So if we can't verify scientific truths, how do we make scientific progress?
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In Popper’s view, science can only progress through trial and error. Scientific conclusions can be compared with each other and experimentally tested for the “strongest” or “most withstanding” one. If a theory is compatible with experimental evidence, then the theory has, for the time being, “passed the test”. However, if the theory’s conclusion has been falsified by experimental evidence, then logically, the theory it has been deduced from has also been falsified. The scientific community hence advances to the next withstanding theory. The longer the period that a scientific model lasts without being falsified, the more likely it is to be true, even though it can never be proven as a certainty.

Falsification within the Scientific Method

Popper’s work seems to shine a light on possible methodical flaws in previously established scientific theories. Psychologist Sigmund Freud, for example, was a target of Popper’s criticism, for what he labelled as “pseudoscientific” work. Freud’s theories, in the eyes of Popper, were “unfalsifiable” - they could never be disproved by new scientific evidence due to their adaptive nature. Hence, in Popper’s view, unfalsifiable theories such as those of Freud ought not to be labelled as scientific. This view can be extremely problematic for many scientific thinkers whose work cannot be conclusively falsified by experimental evidence. Crucially, this view raises the question of what we can qualify as 'science', emphasising the importance of an established and refined scientific method. 

"In so far as a scientific statement speaks about reality, it must be falsifiable; and in so far as it is not falsifiable, it does not speak about reality." - Karl Popper

Popper’s work has been immensely influential in the formation of the scientific method we hold today. Whilst we may have convincing evidence for certain theories, the scientific community can never label them as absolutely “certain”. Instead, the community amends, reforms and re-tests hypotheses to the best of their ability. Theories we hold become more and more probable, but are never established with certainty. Though induction undeniably still plays a major role in the scientific method (else we could not utilise experimental evidence in our reasoning), the awareness that inductive reasoning cannot possibly establish certainty is of critical importance. Among a few other incredible thinkers (David Hume, Thomas Kuhn, etc.), we largely have Popper to thank for the advancement of the scientific method with regards to establishing certainty.

sources:
readings from -
Conjectures and Refutations by Karl Popper
The Logic of Scientific Discovery by Karl Popper