Life is so various that, apparently, nothing can be predicted. In the ancient time even the simplest natural phenomena seemed to people something inexplicable, and, above all - accidental. However, at some stage of development of science the concept of mechanical determinism was born.
Determinism
The principle of determinism means that any phenomenon has to have the reason. And it is unimportant about what phenomena it is. That is the determinism in principle means predefiniteness. Thus, any current state of any system results its previous or initial of states. The principle of determinism rejects all accidents and probabilities. It says that, knowing an initial state, it is possible to predetermine the unambiguous future precisely.
Mechanical determinism
The mechanical determinism is, actually, a subsection of the general concept about determinism, only in relation to the mechanical phenomena in the nature. Otherwise the mechanical determinism is called Laplace determinism in honor of his author. As the example most clearly illustrating the principle of mechanical determinism it is possible to consider the movement of a body. The mechanical determinism says that, knowing initial position of a body and its initial speed, it is always possible to find position of a body in any other timepoint. Thus, the mechanical determinism confirms existence of the equation of the movement of a body.
Modern understanding of mechanical determinism
This principle strictly held positions until scientists went deep into understanding of laws of a microcosm. Upon transition to a microcosm it becomes clear that it is impossible to predict the movement of each particle of some macrobody, the quantity of particles corresponding to macrocosm scales in proportion to ten in the twenty third degree. And trajectories of particles in a microcosm change a huge number of times, and the reasons of their change are almost unpredictable.
Such motion of particles is called Brownian. However this crisis of mechanical determinism existed not for long, to be exact, until James Clerc Maxwell famous for the equations of electrodynamics did not suggest to describe behavior of a large number of particles statistically. Since then views about whether the mechanical determinism lamented or not, were divided. What gave introduction of statistical laws? On the one hand, now it is possible to predict exact value of probability, say, of finding of particles in a certain place. From here it is possible to find also such macroscopic parameters as pressure, density if to speak about gas and to mean Boltzmann's distribution. On the other hand, not clearly, whether exact definition of a condition of particles means exact predetermination of probability? Opinions in this respect still differ.