Lester introduces the Popperian theory of “critical rationalism,” which holds that all knowledge is ultimately only fallible theory.

J. C. Lester is a philosopher specializing in libertarianism. Apart from articles, dialogs, and book chapters—many available online—he is the author of Escape from Leviathan: Libertarianism without Justificationism (paperback 2012) and Arguments for Liberty (2011).

Put simply and starkly, critical rationalism is the view that absolutely all alleged knowledge is ultimately only fallible theory: mere guesses that we can test but which never become more probable by passing those tests. No truth is ever established to any degree at all. What follows can only outline an explanation of this counterintuitive view.

It is part of common sense for people to demand that unusual views, such as libertarian anarchy, must be proved, verified, justified or at least somehow supported (if they are not simply dismissed outright for being ‘absurd’ or extreme); however, no such demands are usually taken seriously with most people’s own favored views. If Karl Popper’s (1902–1994) critical‐​rationalist epistemology is correct, then they are demanding what is logically impossible

Popper was originally interested in the demarcation between science and non‐​science (not science and nonsense, as is sometimes thought). It cannot be true that scientific theories are epistemologically verified or justified (the general term he prefers to cover all types of foundationalism: the view that knowledge is supported in some way), because such universal (hence infinite in scope) theories could never be supported by a finite amount of evidence—even if all that evidence were unproblematically accurate. Thus there is no solution to David Hume’s (1711–1776) restatement of the epistemological problem of induction. Induction as an epistemology is a myth, just as was its original logical form in Aristotle (c384‐​322BCE) as the supposed inverse of deduction. The popular insistence that there is some form of induction and justification nevertheless, is a futile attempt to refute with common sense a philosophically argued conclusion.

But Popper noticed a crucial asymmetry: the falsification of universal theories is logically possible; we need just one counter instance. ‘All swans are white’ cannot be verified by any finite number of positive instances of white swans. It can be falsified by one instance of a non‐​white swan; as this ‘well‐​supported’ theory eventually was falsified by the discovery of black swans in Australia. So, methodologically, we can make a virtue of producing bold universal conjectures that we do not pretend are ultimately supported by evidence and then test these conjectures as severely as we can: both by observation and criticism. We can happily admit that, in principle, we might be mistaken about any theory regardless of the amount of testing. This became known as ‘falsificationism’.

Consider some relevant implications of this view. There is no reason to think that we are in fact mistaken about any particular theory unless we find an apparently good counter instance or criticism of it. So skepticism must be maintained in the sense that knowledge is always uncertain, but not in the sense that knowledge is impossible: we often possess theories that are true. Metaphysical theories are merely empirically unfalsifiable but they may be true. And all scientific theories have metaphysical presuppositions or consequences. Apparently singular observations are also both theory‐​laden and have infinitely many consequences. Thus they too are in the situation of not being verifiable; though Popper himself sometimes writes of the ‘confirmation’ of single instances. This view is not to deny that probabilities exist, but only to imply that they too do so within the framework of what are ultimately mere conjectures. Critical rationalism is both descriptive and prescriptive. It describes what we have to be doing to do science at all: conjecturing and testing. But it also prescribes how to do science better: bolder conjectures and more rigorous tests.

Critics sometimes suggest that falsificationism is not falsifiable, and so fails by its own standards. It is true that it is not empirically falsifiable, though it is criticizable, but an epistemological theory is not supposed to be a scientific theory. Philosophy is not science. Some critics also object that one cannot conclusively verify the counter instance either, so falsification is also impossible; alternatively, that if falsification is possible then to falsify a universal theory is thereby to verify its negation, so that some verification is possible too. However, it is part of falsificationism that a ‘justified’ falsification is not possible. Putative falsifications are themselves conjectures that remain open to testing; though we can test only one thing at a time and all tests assume much. The point is that we could, in principle, observe a single counter instance of a universal theory (see a black swan) while we could not, in principle, observe verifying instances (see all swans, at every time and place, being white). So as a falsification is at least possible we are, as before, entitled to conjecture that we have discovered a falsification if we cannot seem to refute it. But we never leave the realm of conjecture.

Partly thanks to the critical work of other philosophers than Popper, this falsificationist epistemology has been extended to mathematics, logic, morals and every other area of knowledge; and has become known as ‘critical rationalism’. Outside the empirical sciences the method is about actively and unceasingly seeking criticism with the rejection of any kind of epistemological foundations; even in logic and mathematics: a valid proof has no more force than its assumptions. Assumptions or conjectures are all we have to go on in all areas of knowledge.

It is possibly pedantic to eschew all ‘justificationist’ expressions in everyday speech, especially arguing ‘for’ (i.e., supporting) a theory: it would be like refusing to say ‘sunrise’ because that contradicts the idea that the Earth goes around the Sun. It is sufficient that one understands and makes plain that a theory can ultimately remain only a conjecture and that such arguments can only properly elaborate the consequences of, or apparent evidence about, a theory; which is useful for understanding it and stimulating criticism. Many alleged ‘justifications’ are merely just such explanations and elaborations.

Perhaps there is at least one non‐​foundationalist usage of ‘justified’ that critical rationalists can use consistently. This is simply in the sense that some thesis has been ‘squared’ with the apparent facts and any criticisms. In other words, the thesis appears to be without problems. But this is not to say that it is positively supported in any way or that it will remain apparently ‘justified’ even in this sense.

If critical rationalism is thought not, exactly, right, then seeing which theories withstand critical scrutiny can still be accepted pragmatically as a useful way to deal with theories; even by justificationists who cannot agree about which theories are justified and how. This practical point is not to minimize the theoretical differences. The classical view of knowledge is of justified, true belief. Critical rationalism denies that justification is possible, observes that most important scientific theories will not be true, and holds that belief is irrelevant. Thus the critical rationalist view of knowledge has been humorously explained as unjustified, untrue, unbelief.

This essays is excerpted from “The Dictionary of Anti‐​Politics” (forthcoming).