In a 3D diagram whose coordinates are V, T and P, the points in the P-V-T space which represent the equilibrium states of existences of the system lie on a surface.
Consider a process which moves the gas from state 1 to state 2, the volume of the gas is changed by V =V2-V1.
How many paths could it proceed along?
A lot!! e.g. path 1a 2 or
Path 1 b 2