In the present paper the force of crystallization is defined mathematically by help of elementary physico-chemical considerations. Every crystal is, as known, able to execute a linear pressure of growth when being in diffusive communication with a supersaturated milieu. At a given supersaturation (as compared with the saturation at zero pressure) the different crystals execute different pressure of growth. On the other hand it is evident that the pressure which a given crystal is able to bear and grow against rises with the degree of supersaturation. Therefore, the linear force of crystallization of a certain crystal is defined as the pressure which the given crystal is able to bear or grow against at a given degree of supersaturation.