By an extension of the Yang-Lee picture of phase transitions to the case of two complex variables, we have been able to study the properties of a ferromagnetic system in the vicinity of the critical point. A linear approximation is used, which yields a satisfactory result close to that point. Especially, we see how a critical point and a phase boundary can arise from statistical mechanical laws. It is shown that scaling laws are generally valid, although there may be special cases when they are not.