The demarcation problem in the philosophy of science is about how and where to draw a the lines around science. The boundries are commonly drawn between science and non-science or science and pseudoscience. A form of this problem, known as the generalized problem of demarcation subsumes both cases. The generalized problem looks for criterion for deciding which of two theories is better. The better theory being the more scientific.

After more than a century of active dialogue, the question of what marks the boundary of science remains fundamentally unsettled. Nonetheless, reasonable consensus exists on certain sub-issues. Criteria for demarcation have traditionally been coupled to one philosophy of science or another. Logical positivism, for example, espoused a theory of meaning which held that only statements about empirical observations are meaningful, effectively asserting that statements which are not derived in this manner (including all metaphysical statements) are meaningless. Later, Karl Popper attacked logical positivism and introduced his own criterion for demarcation, falsifiability. This in turn was criticised by Thomas Kuhn, and also by Popper supporter Imre Lakatos who proposed his own criteria that distinguished between progressive and degenerative research programs.

Kuhn and paradigm shifts

Thomas Kuhn, an American historian of science, has proven very influential in the philosophy of science, and is often connected with what has been called postpositivism or postempiricism. In his 1962 book The Structure of Scientific Revolutions, Kuhn divided the process of doing science into two different endeavors, which he called normal science and extraordinary science. The process of "normal" science is what most scientists do while working within the current accepted paradigm of the scientific community, and within this context Karl Popper's ideas on falsification as well as the idea of a scientific method still have some currency. This sort of work is what Kuhn calls "problem solving": working within the bounds of the current theory and its implications for what sorts of experiments should or should not be fruitful. However, during the process of doing "normal" science, Kuhn claimed, anomalies are generated, some of which lead to an extension of the dominant paradigm in order to explain them (like the idea of punctuated equilibrium within the paradigm of evolution), and others for which no satisfactory explanation can be found within the current paradigm. When enough of these anomalies have accumulated, and scientists within the field find them significant (often a very subjective judgment), a "crisis period" is began, and some scientists begin to participate in the activity of "extraordinary" science. In this phase, it is recognized that the old paradigm is fundamentally flawed and cannot be adapted to further use, and totally new (or often old and abandoned) ideas are looked at, most of which will be failures. But during this time, a new paradigm is created, and after a protracted period of "paradigm shift," the new paradigm is accepted as the norm by the scientific community and integrated into their previous work, and the old paradigm is banished to the history books. The classic example of this is the shift from Maxwellian/Newtonian physics to Einsteinian/Quantum physics in the early 20th century. If the acceptance or failure of scientific theories relied simply on simple falsification, according to Kuhn, then no theory would ever survive long enough to be fruitful, as all theories contain anomalies.

The process by which Kuhn says a new paradigm is accepted by the scientific community at large does indicate one possible demarcation between science and pseudoscience. Richard J. Bernstein reads Kuhn as saying that a new paradigm is accepted mainly because it has a superior ability to solve problems that arise in the process of doing normal science. That is, the value of a scientific paradigm is its predictive power and its ability to suggest naturalistic solutions to new problems while continuing to satisfy all of the problems solved by the paradigm that it replaces. Pseudoscience can then be said to be demarcated by a failure to provide such naturalistic explanations, which leads to the labeling of any theory represented as science and appealing to metaphysical explanations for natural phenomena as a pseudoscientific idea.

Feyerabend and the problem of autonomy in science

There has been a post-Kuhn trend to downplay the difference between science and pseudoscience, as Kuhn's work largely called question to the Popperian ideal of simple demarcation, and emphasized the human, subjective quality of scientific change. The radical philosopher of science Paul Feyerabend took these arguments to their limit, arguing that science does not occupy a special place in terms of either its logic or method, and so that any claim to special authority made by scientists cannot be upheld. This leads to a particularly democratic and anarchist approach to knowledge formation. He claimed that there can be found no method within the history of scientific practice which has not been violated at some point in the advancing of scientific knowledge. Both Lakatos and Feyerabend suggest that science is not an autonomous form of reasoning, but is inseparable from the larger body of human thought and inquiry. If so, then the questions of truth and falsity, and correct or incorrect understanding are not uniquely empirical. Many meaningful questions can not be settled empirically -- not only in practice, but in principle.

According to this way of thinking, the difficulty string theorists have had in applying experimental science would not bring in to question their status as scientists.

Conclusion

If observation cannot act as a theory-independent foundation for the scientific enterprise, science becomes a cycle of hypothesising and verification embedded in a theoretical framework and tied to the 'real world' by the agreement of the scientific community. Popper's claim that only falsifiable statements are scientific does not help here (see The Criterion of Demarcation). The Quine-Duhem thesis argues that it is not possible to prove that a statement is falsified; rather, falsification occurs when the scientific community agrees that a statement is falsified.

Assuming this to be true, it is not obvious how scientific debate differs in any logical way from the debates of, for example, historians. Both work within a cycle of hypothesising and verification, historians by reference to historical documents (the past), scientists by reference to the experiments they propose to construct (the future).

One might argue that science occupies a special place because its experiments can be repeated, but using repetition as a demarcation criterion would disenfranchise areas that are at present considered to be science, such as palaeontology and cosmology.

The problem of demarcation is considered solved by some, for others there is no such thing as an autonomous scientific method, no definitive philosophy of science and no clear and agreed-upon distinction between science and pseudoscience.