The scientific method is based on experiments and on the mathematical processing of the obtained data in the form of mathematical equations. The fact that this method allows us to predict the outcome of experiments with mathematical accuracy, gives us the feeling that we completely grasp the physical processes. In this introduction to his papers on the physical nature of the basic concepts of physics such as length, time, velocity, mass, linear momentum, energy, etc., the author demonstrates that this self-confidence is based on a circular reasoning: the experimental data agree with our mathematical equations, because the mathematical equations are quantitative expressions of the experimental data. In that way, the mathematical formulation is not necessarily a description of the physical process, but any description that fits in with the mathematical equation. It is clear that in that way the ‘laws’ of physics, which consist of the mathematical equations expressed in spoken words, will rather give us a logical insight in the mathematical equations than in the underlying physical mechanism. This quantitative approach has thereby led to the use of an impenetrable, trivial terminology, with weird concepts, such as ‘force field’, ‘energy field’, ‘curved space-time’, ‘dark matter’, ‘dark energy’, ‘creation’ and ‘annihilation’ of particles, ‘multiverses’, etc. . To come to a real understanding of the physical processes, the author proposes the approach of a natural elucidating physics’ that allows him to define the physical nature of the basic concepts.