My chemistry textbook tries to explain the properties of solids and liquids with the kinetic theory. Is this not good? Should only gases be explained by the kinetic theory since one of the postulates in this theory is that particles exert no forces on each other. The book had to disable this axiom when explaining solids and liquids and said that the forces increase the closer the particles are. But cancelling an axiom is not good or improper isn't it? But theory should be used to explain solids and liquids in general?