The envelope pressure potentials of the liquid water and ice in a frozen soil are defined. The envelope pressure potential of liquid water is a generalization of the definition of the envelope pressure potential (overburden potential) of the water in an unfrozen swelling soil. In order to express these envelope pressure potentials in terms of volume ratios, use is made of the void ratio, the moisture ratio equivalent, and the ice ratio equivalent. A new development is initiated by the formulation and derivation of the frost potential of both the liquid water and the ice. These frost potentials are expressed in terms of the ice ratio, the moisture ratio, the ice ratio equivalent, and the moisture ratio equivalent. The relations between these variables are intrinsic properties of the porous medium which have to be determined experimentally.