The philosopher of science Federico Laudisa points out an important condition about the principle of causality: "Since the times when the distinction between philosophy and science did not exist either in fact or in law, the evolution of ideas that the Western philosophical tradition did develop in relation to the notion of cause and the principle of causality can be read as a history of the idea of knowledge: a history that has been enriched - and at the same time complicated - since the scientific revolution of the seventeenth century began to diverge the fate and ideals of philosophy and science. "

The principle of causality is based on the idea that phenomena follow each other only in a process of cause and effect, and all that does not respond to this law, is due to chance.

Empirical observation (the experimental method of Galileo to question Nature) guides us in identifying the causal links that underlie the phenomena we observe.

Through the analysis of the causes it is possible to understand the operating mechanisms of the world. Our belief is that the rational intelligibility of reality has an absolute validity and the limiting factor is not inherent to Nature (i.e. the rational tool for understanding reality is limited) but extrinsic, that is, relative to our capacity to interpret reality in only rational terms.

To this deep conviction we have the alleged superiority enjoyed by the so-called Exact Sciences (Physics, Mathematics for example) compared to the Human Sciences (Psychology, Medicine, etc.) as if the latter, the Human Sciences, were not so skilled in identifying the rational thread that binds phenomena, which instead seems so clear in a discipline such as Physics which  is the basis of our knowledge of the world. Not for nothing, we classify certain Sciences exact, as to say that we can not always have satisfied our need for rationality.

But to what extent holds the causal interpretation of reality? If taken to extremes, it comes to a conflict with free will. Each of us is perceived, as an individual, free - within certain limits - to self-determinate. But if the world follows rules that are purely causal, assuming to know the laws that govern the time evolution of the world and the conditions at a given time (the initial conditions) we will be able to predict the future of the world ... including ourselves. This made someone think (the most vocal proponents of a deterministic interpretation of reality) that our self-determination be in reality only apparent and illusory, contrary to what we seem to perceive.

We should consider one important fact. Together with the theory of relativity and non-Euclidean geometry, quantum mechanics is a real difference in respect to the traditionally deterministic vision of the world handed down from the time of Newton. As Einstein demonstrated the inaccuracy of the laws of classical mechanics, physicists that became interested in quantum mechanics showed how in the world of the infinitely small definitions of wave, particle, position, were tight to the new "quantum objects" like the electron and photon, and that they could be used for a rough definition, borrowed from classical mechanics, which, however, certainly did not return faithfully the physical essence.

Another upsetting fact  was the elimination of the principle of causality: quantum mechanics, in contrast to the Newtonian mechanics, does not offer certainties, but is based on a probabilistic view of physical events, that does not derive from the need to synthesize the behavior of a very large number of elementary particles that individually behave in a deterministic way. Thanks to the formulation of the indeterminacy principle, probability becomes an intrinsic characteristic of every single quantum object, whose behavior is always subject to a margin of uncertainty. It is however necessary to distinguish between the subjective case and the objective one.

We are facing an event subjectively random when the cause is unknown, but this should be there. The objective randomness characterizes a phenomenon of which not only the cause is unknown, but it is not there, and its absence is not due to a lack of our system of investigation but to the presence of a pure coincidence, a situation that cannot be seen in the principle of correlation between cause and effect, an idea that despite being very effective in interpreting the physical world, is always the result of the fact that men to understand the world dictate to it their conceptual schemes.

But in the case of quantum mechanics, the principle of causality is quite helpless. This uncertainty on the fundamentals of matter, the microscopic objects, dealt by quantum mechanics, might suggest a world ruled by chance. This idea has been discussed also by several philosophers.

It meets the Heisenberg uncertainty principle, which says that the laws apply, but they don’t because we can not know with absolute precision the status of the system. The indeterminacy with which we can know the position and velocity of a particle is no longer a lack of measuring instruments but are due to the characteristics inherent to nature: nature in a sense rebels to be known and reserves a degree of freedom. From the Heisenberg indeterminacy principle rises, almost magically, our self-determination: consider a system that contains a conscious subject. If we were able to predict the evolution of a deterministic system the result would be that the subject did not self-determine, with an obvious absurdity. (It is for this reason that studies of consciousness and mental functioning link the characteristics of the conscious subject to quantum indeterminacy).

The experiments on the particles reveal to a certain extent the non-existence of a causal principle and an almost complete statistical freedom of the results of the experiments. In the sense that 100 electrons launched all with the same direction and the same velocity will go to 100 different places contrarily than a billiard ball that will end up in the same hole all 100 times . And what about our idea of predicting the evolution of the system, preparing it in a certain state? We know that temporally according to some premises certain results follow, and the observation that chronologically things always behave in the same way  leads us to think that there is a causal link. Common sense brings us in this direction because of the facts of every day life, no one would doubt. This no longer seems true for the fine structure of reality, the particle physics, field of investigation of Quantum Mechanics. But, then, where is the catch? Where we go wrong?. At large , we know that the analysis cause – effect works, and where does it go when we reach the size of the electron and we are met by the Heisenberg indeterminacy that makes us change each time the result of the experiment? Must we give up causality? It no longer applies and why?