When we say that something is scientific, we tend to imply that it is authentic, clear and safe. Why, everyone wants that their area of expertise will be treated as a scientist. Other fields of study are qualified as pseudo-ciencientificos or false science, whose practitioners are called to their scientific activity and even used scientific language. But, how you can separate scientific from what is not? It is not easy task. Delimit the boundaries of science would be a job without exito1. This border that separates the science of the pseudo-ciencia is defined by the criterion of demarcation used. This has been debated for many scientists and philosophers of science of the 20th century. Kant stated that the judgments which constitute all science must be synthetic a priori. Synthetic because they must be extensive, i.e., our knowledge of science has to be expanded. And a priori because its truth cannot depend on experience, which is particular, not universal; in this way they are also necessary. This is an example of a criterion of demarcation. As such deprive other knowledge be called scientists. Another criterion of demarcation would be that established the Vienna Circle: is only a scientist what is empirically verifiable. That which cannot be proven by the experience it is neither true nor false, meaningless, it is not scientific. Popper critic expressed at the Vienna Circle. His criterion of demarcation was based on Falsifiability. This establishes that continuously verifying a theory useless to test its validity because there may be an object that has not been subjected to analysis and that belies that theory. Many checks do not prove the absolute validity of a theory, but a single one that refuted it invalidates it. For example, if we see one, two, three white swans, we dare to say: all swans are white. But at the moment that we saw one black, our theory would be false.