In defining the path of scientific progress there might be a problem of demarcation, a concept proper to philosophy of science, as well as a cardinal principle of epistemology, which aims to define the limits of science. The problem arose from the difficulty of distinguishing science from pseudoscience and metaphysical questions of philosophy.

Despite the age-old debate on this topic, it was impossible to find a solution universally accepted by scientists and epistemologists. To discover what distinguishes a scientific theory from other types of knowledge can give scientists a good criterion to develop existing theories, without running the risk that scientific research should result in pseudoscience. It is necessary, in fact, to have a certain, unequivocal criterion in order not to stray beyond the limits of science.

Popper puts it this way: "The criterion of demarcation inherent to inductive logic – i.e. the positivist dogma of meaning - is equivalent to the demand that all the statements of empirical science (or all " significant " assertions) should be subject to a final decision regarding their truth and falsehood; we’d say that they should be deductible in a conclusive way. This means that their shape should be such that both to verify and to falsify them should be logically possible. Thus Schlick declares: "[...] an authentic assertion must be subject to final verification"; Waismann states even more clearly: "If there is no way to determine whether a statement is true, then it is meaningless. In fact, the meaning of a statement is the method of its verification ".                                                          

"Now, in my opinion, there is nothing similar to induction. It is therefore logically unacceptable the inference from singular statements "verified by experience" (whatever that might mean) to theories. So the theories are never empirically verifiable. If we want to avoid the mistake of positivism, of eliminating through our criterion of demarcation systems theories of the natural sciences, we have to choose a policy that will allow us to admit, in the domain of empirical science, even assertions that can not be checked”.

"But I - Popper continues - certainly will admit as empirical or scientific, only a system that can be controlled from experience. These considerations suggest that, as a criterion of demarcation, you should not take verifiability but falsifiability of a system. In other words: from a scientific system I will not demand that is capable of being chosen, in a positive sense, once and for all; but I will demand that its logical form is such that it can be highlighted, by means of empirical controls, in the negative sense: an empirical system must be in the condition to be refuted by experience. "

"It could be tried to turn against myself the criticism that I addressed to the inductivist criterion of demarcation: it could seem that against falsifiability as a criterion of demarcation be possible to raise criticisms similar to those that I, for my part, raised against verifiability “.

“This attack can not annoy me. My proposal is based on an asymmetry between verifiability and falsifiability, asymmetry resulting from the logical form of universal statements. These, in fact, can never be derived from singular statements, but can be contradicted by them. Therefore it is possible, by means of purely deductive inferences (with the help of the ‘modus tollens’ of classical logic), conclude from the truth of singular statements to the falsity of universal statements. Such reasoning, that  concludes the falsity of universal statements, is the only type of strictly deductive inference processing, so to speak, in the "inductive direction '; that is, from singular statements to universal statements.

That said, let us return to the concept of progress. After more than a century and a half of debate, in the second half of the twentieth century, the discussion was characterized by examining the practical aspects of an epistemological and heuristic nature of scientific activity. Also the semantic components of the idea of progress were specified: 'advance', 'change', 'improve'. Advance does not necessarily mean to improve; even the change is not a progress, since progress, setbacks and declines alternatively meet.

It was noted that progress could not be assumed nor postulated, but required, each time, epistemological evaluations that are not mathematical measurements. With this, dogmatisms fell on linear and cumulative progress of science, on the ‘indisputability’ of scientific truths and its methodological validity.

Such a view of the progress of scientific theories can be summarized: changes in meaning and reference remain closely tied together. They mark a progress only if they result in a determination in the semantic shift from one theory to another. The hermeneutic conception shows the scientific knowledge as a 'spiral' where past applications of terms, concepts and methodological principles are essential to understanding the new ones. This 'hermeneutic spiral' can best judge the scientific theory that can unite the other in a coherent whole and arrange them according to a historical understandable narrative.

A second perspective is in some respects similar, but setting the problem in different terms. An important aspect has to be highlighted. Given that one can speak of philosophic thought progressive or regressive, only in the local sense, logic is considered indispensable but insufficient. Deductive reasoning is valid only for the 'scientific theory', not for ' scientific dynamics’, which requires instead the argumentative form.

The problem of scientific progress would be resolved by the notions of "semantic area ", "intentional network" and "real network". The semantic area would be the set of rules summarized in the concept and sufficient to grasp the meaning. The more it is wider, the more you can grasp the meaning of the concept, possibly made up of a "knowledge network". Hence the concepts of "network". " Intentional network " is the interlacing of the intentional properties, whose nodes are given by the relevant entities; "Real network" is the intertwining of real properties, whose nodes are the real entities.

To know an object, therefore, it is necessary to have a concept with which identify it and a semantic area in which to place it. Suffice it to intentional entities. For the real ones, however,  the experimental procedures are also required. Knowing the intentional, then, is to build, among the elements of the intentional level, the same relationships put up between the elements of the conceptual level.

Knowing the real means to impose a subset of intentional relations, so as to form real relationships between real entities. Any theory, therefore, is a portion of a conceptual network or a part of an interdependent whole. Therefore, the construction of a new scientific theory does not totally displace the old one, nor does it require its disappearance.