It can be applied for system in equilibrium only. Consequently, it is of little value in case of very slow equilibrium state attaining system.
It applies only to a single equilibrium system, and provides no information regarding any other possible equilibria in the system.
It requires utmost care in deciding the number of phases existing in an equilibrium state, since it considers only the number of phases, rather than their amounts. Thus, even if a trace of the phase is present, it accounts towards the total number of phases
It conditions that all phases of the system must be present simultaneously, under the identical conditions of temperatures and pressure.
It conditions that solid and liquid phases must not be in finely-divided state, otherwise deviations occur.
In phase rule, various variables are temperature, pressure and composition. This phase rule does not consider the electric or magnetic influences. If such variables are considered, the factor 2 of the phase rule has to be adjusted accordingly.