It is now generally recognised that there are two main types of laws. Laws of the first type establish a simple correspondence between two or more parameters; they are fulfilled in each individual case (usually only approximately in real phenomena but we shall not consider this question here). There are different names for this type: "dynamical", "deterministic", "causal"," simple", "nonstatistical" etc. Laws of the second type are fulfilled only by large sets of events. They are called" statistical", sometimes "probabilistic" or" stochastic". Here we shall consider only the latter type.