Falsificationism starts with the rejection of induction as a basis for scientific knowledge, which it regards as irrational despite being a part of scientific method. Since science cannot be irrational, there must be another way for scientific method to proceed.

Karl Popper suggested that scientific knowledge is a category that is falsifiable, rejecting metaphysics, much of psychology, existential statements (e.g. "there are such things as electrons") and so on.

Critically evaluate Popper's falsifiability criterion of demarcation

Popper developed the theory of falsification in response to the problem of induction. He supposed that induction cannot be part of rational thought, but that we cannot be irrationalist about science, and so we must be able to find another rational (deductive) foundation for scientific knowledge and method. This was falsificationism, according to which a theory cannot be proved true but it can be falsified, allowing scientists to progress by removing false hypotheses. Because of the dogmatic limits of this demarcation criterion, Popper and his followers also developed a methodology and set of criteria for evaluating falsifiable but unfalsified hypotheses. Ultimately, Popper's criterion of demarcation is too dogmatic to work, and the tertiary methodology and criteria leave him open to the very criticism that he leveled on induction.

The basis of Popper's theory, as I have said, is that we cannot infer new truths, but we can infer that a theory is false. If we observe a set of phenomena, it would be irrational to induce that a hypothesis that predicted the phenomena is true. If, however, the set of observed phenomena contradict the hypothesis, because we can be sure of our observations – Popper was an empiricist – we can be sure that the hypothesis must be false. Popper then took this statement and suggested that if a hypothesis is falsifiable, and it has not yet been falsified, then scientists can in some way accept or at least preserve it in their system of theories. Moreover, he claimed that an unfalsified falsifiable hypothesis is in some way close to the truth, and that the more stringent the testing of the hypothesis, the closer to the truth it must be. The body of science therefore consists in all the theories that are falsifiable and not false (Lakatos, p. 12). And within this body of science, proximity to the truth is a methodology available to discerning scientists. This approach borders on making truth semantically meaningless in science, which can either be a serious problem or an acceptable consequence.

The falsifiability criterion immediately raises the question: what is it for a hypothesis to be falsifiable? For an empiricist like Popper, the obvious answer is that it can, in principle, be tested experimentally such that a set of observations could conceivably contradict it. But how can we know if it is possible for us to experimentally test a hypothesis? We may think it possible but fail to construct an appropriate experiment, even after a thousand years of attempts. But this doesn't mean that in principle it isn't falsifiable... the simple possibility that it is false makes it so. The falsifiability criterion was supposed to mark scientific theories as distinct from metaphysical theories, since the latter are not in principle falsifiable. But it seems problematic.

A solution offered by Lakatos was to say that it must be falsifiable with available scientific methods (Lakatos, pp. 12-13). But even here, the methodology raises problems.

To begin with, it isn't clear that we can distinguish so clearly between observation statements and theories. Most scientific “observation” is done with the help of instruments, and that data that is collected is then interpreted with the help of theories. So if scientists must accept observation statements, they must also be able to accept the theories upon which they are based. But according to Popper's dogmatic falsificationism we cannot accept theories as being true. Furthermore, both in theorising and observing the scientist will have expectations and hypotheses that are based on both past theory and past observation. So we cannot use pure observation as a basis for scientific methodology (Lakatos, pp. 14-15).

To make things even more problematic for Popper, elementary logic – which he used as the basis for his rejection of induction – dictates that propositions can only be derived from other propositions. Observations cannot, therefore, have any logical bearing on propositions and so cannot form the basis for falsification (Lakatos, pp. 15-16).

A further problem with falsificationism is, again, with the use of observation statements. If a scientist formulates a hypothesis and then finds conflicting evidence, E1, he can always posit the existence of a second unobserved phenomenon, E2, that will save his hypothesis. For example, a planet whose orbit appears distorted – from its expected ellipse – could be under the gravitational influence of another large mass like another planet. If we charitably assume that there are no further factors that could be taken into account, and that the scientist then takes E2 into account he cannot be sure about E2 until it is observedand so cannot use it to support the hypothesis. If he fails to observe E2 and thereby falsifies his hypothesis, we must conclude that the conjunction E1 of E2 falsified the hypothesis, not E2 alone, which requires us to be certain about the truth of both E1 and E2.

In reality, the set of evidence will include E1 and E2 and E3...n where n can be any number. Now the scientist must find a way to test each of the pieces of evidence in isolation, or rather in an experiment in which none of the other pieces of evidence are factors, to establish which of the pieces of evidence is false. This can only be satisfactory by Popper's pragmatic standards if n is small and if E1...n can all be separately falsified, i.e. if you have falsified a sufficiently small set of evidence that the result yields scientific insight.

Popper's solution to these problems, which make dogmatic falsificationism unviable, was to adopt a conventionalist stance, creating methodological falsificationism. According to conventionalism, we can accept a statement as being “true” if there is general agreement amongst the community of intellectuals studying it. So if scientists can reach a general agreement about a particular observation statement they can claim it is “true”, therefore allowing them to “falsify” hypotheses. Note the qualification on the terminology of falsificationism – Lakatos emphasises that by Popper's strict logical standards we cannot claim that “true” observation statements in this sense are true, so we must qualify the entire body of terminology (Lakatos, p. 23).

But if a general agreement amongst scientists can establish a convention, which in turn can, though revisable, “falsify” a hypothesis, why can scientists not also “prove” a hypothesis through “induction” based upon convention? (Bird, p. 242) In other words, if we can weaken falsificationism to this extent, can we not also accept a similarly weakened form of induction? Popper could still reject this move on the basis that a weakened falsificationism is still stronger than a weakened inductivism because it is closely related to deduction.

An important consequence of this methodological falsificationism is that all observation statements must be considered revisable. We cannot, therefore, “disprove” a hypothesis, we can only reject it. A critic who wanted to preserve a strict criterion of epistemological justification would object that Popper has therefore failed. But Popper would reply that methodological falsificationism is pragmatic, in accordance with scientific method. If we are to reject induction and preserve the empiricist basis of scientific method, Popper suggested, this is the only route available.

If we accept, for the moment, Popper's framework for the problem of demarcation – providing a sound, pragmatic basis for scientific method – we still find methodological falsificationism wanting. Take the probabilistic methodology, for example. If we have a hypothesis that in a certain experiment a result will occur at a rate of 75%, and the experiment is accepted as a convention, then we can falsify statement of the form: “the rate of occurance is greater than 80%” and “the rate of occurance is less than 70%” and thereby deduce that the rate is 75±5. But according to Bird, this is simply a strong form of induction, which means that Popper's criterion of demarcation relies on induction “when the going gets tough” (Bird, p. 180)

Popper might reply that the observations corroborate the hypothesis and indicate a proximity to the truth, whereas induction must always confirm a truth. Popper is therefore giving a pragmatic basis for preference on top of his criterion for demarcation. One could say then that falsificationism provides a strong rational basis for science, from which methodological falsificationism can provide a basis for scientific method. Bird, however, isn't convinced.

Popper formulated this proximity to the truth, which he called verisimilitude, in the following way: We have two propositions, A and B, which are close to the truth, proposition T. Assume that A is closer to T than B, that A is greater than B, and that T is greater than A:

1.(T – A) > (T – B)
2.A > B
3.T > A

In all formulations of A, B and T, A will have more true consequences than B, and so can therefore be said to have a greater verisimilitude. In other words, “the true consequences of B are included among the trust consequences of A; and the false consequences of A are included among the false consequences of B” (Bird, p. 244). This provides a rational answer to the problem of probabilistic statements, but only where the consequences of the statements in question are comparable. Where hypotheses predict different kinds of consequences, this formulation cannot provide any indication of relative verisimilitude. This means that the criterion of demarcation, upon which this notion is based, is again reduced to an extremely strict, dogmatic falsificationism that cannot provide a rational basis for scientific method.

There is one further worry for falsificationism in general. The method depends upon scientists starting with a set of hypotheses and subjecting each to scrutiny, whittling the body of hypotheses down and thereby making progress. But scientists evidently create more hypotheses as they work, expanding the body rather than reducing it. And if we accept the linguistic assertion that language is creative, then there are, theoretically, an infinite number of hypotheses that scientists can try to falsify. So in terms of methodology, Popper can offer little in the way of insight; he claims that “coming up with a hypothesis is an exercise of the imagination” (Bird, p. 239), And as a criterion of demarcation, it can only say what is and what isn't scientific by reference to the possibility of experimental testing with available methods; in other words it cannot mark a limited body of hypotheses as constituting the body of scientific knowledge, nor even of “scientific” knowledge.

So to conclude, Popper's falsifiability criterion of demarcation seems attractive insofar as it rejects inductivism and accords to an extent with scientific method. But both as a criterion of demarcation, and as a basis for a scientific methodology – something it ought to be able to provide – it seems to either fall back on inductivism or to undermine the place of empiricism in science. The most it can offer is a new category of “science” that is pragmatic but philosophically tangential to science.

Bibliography

A.Bird, Philosophy of Science, (London: Routledge, 2003)

I.Lakatos, The Methodology of Scientific Research Programmes: Philosophical Papers, Volume 1 (Cambridge: Cambridge University Press, 1978)

W.H.Newton-Smith, A Companion to the Philosophy of Science, (Oxford: Blackwell, 2001)