Karl Popper Quotes

A theory which is not refutable by any conceivable event is non-scientific. Irrefutability is not a virtue of a theory (as people often think) but a vice.

No amount of experimentation can ever prove me right; a single experiment can prove me wrong.

A good scientific theory is one which is falsifiable, which has not been falsified.

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.

The criterion of the scientific status of a theory is its falsifiability, or refutability, or testability.

In science, if an idea is not falsifiable, it is not that it is wrong, it is that we cannot determine if it is wrong, and thus it is not even wrong.

There can be no ultimate statements science: there can be no statements in science which can not be tested, and therefore none which cannot in principle be refuted, by falsifying some of the conclusions which can be deduced from them.

It is certainly not the least charm of a theory that it is refutable.

A system is empirical or scientific only if it is capable of being tested by experience. These considerations suggest that not the verifiability but the falsifiability of a system is to be taken as a criterion of demarcation... It must be possible for an empirical or scientific system to be refuted by experience.

Science does not limit itself merely to what is currently verifiable. But it is interested in questions that are potentially verifiable (or, rather, falsifiable).

Falsifiability for a theory is great, but a theory can still be respectable even if it is not falsifiable, as long as it is verifiable.

Theories are not rejected by cirsumstantial evidence: it takes a theory to beat a theory.

Another thing I must point out is that you cannot prove a vague theory wrong.

The theory must not contradict empirical facts.

Propose theories which can be criticized. Think about possible decisive falsifying experiments-crucial experiments. But do not give up your theories too easily-not, at any rate, before you have critically examined your criticism.

There never comes a point where a theory can be said to be true. The most that one can claim for any theory is that it has shared the successes of all its rivals and that it has passed at least one test which they have failed.

The strength of a theory is not what it allows, but what it prohibits; if you can invent an equally persuasive explanation for any outcome, you have zero knowledge.

Whenever a true theory appears, it will be its own evidence. Its test is, that it will explain all phenomena.

I think that we shall have to get accustomed to the idea that we must not look upon science as a 'body of knowledge,' but rather as a system of hypotheses; that is to say, as a system of guesses or anticipations which in principle cannot be justified, but with which we work as long as they stand up to tests, and of which we are never justified in saying that we know they are 'true' or 'more or less certain' or even 'probable.'

Scientific research can reduce superstition by encouraging people to think and view things in terms of cause and effect.

When I worked on the polio vaccine, I had a theory. I guided each [experiment] by imagining myself in the phenomenon in which I was interested. The intuitive realm . . . the realm of the imagination guides my thinking.

If the evidence says you're wrong, you don't have the right theory. You change the theory, not the evidence.

A single test which proves some piece of theory wrong is more valuable than a hundred tests showing that idea might be true.

We think very few people sensible, except those who are of our opinion.

We have reached a situation where a theory has been accepted as fact by some, and possible contrary evidence is shunted aside. [This is] mythology rather than science.