Many investigations do not prove the absolute validity of a theory but one that refutes the void. For example, if we see one, two, three … white swans, we dare say: "All swans are white." But when we saw a black, our theory would be false. However, we could say: "All swans are white." Thus science advances. Walk to the right but not the extent, but subject to refute a theory, will be closer to the truth than before.
Therefore, cataloging a pseudo-scientific argumentation depends on the demarcation criterion we use. For example, if we want to know if metaphysics is a science, as Kant would be if their judgments are synthetic and a priori. If we subject the criterion of demarcation of the Vienna Circle, not a science because its conclusions can not be verified empirically. Popper does not qualify as the science, but accept that logic holds between their judgments and that they are rational criticism (although not empirically). But we must not overlook is that the metaphysical realities that are not sensitive, that would be absurd to prove his worth in a field that is not applicable.
Therefore, it is now widely accepted demarcation criterion separately in each science and which is based on: logical consistency (or internal), controllability of the precise statements and symbolic (clearly define what you mean each concept or item used). Each science will give different significance to each of these three criteria. As a result, the scientist can know the degree of certainty in the science that lies under study.