Abstract: It is obvious that the exact solutions of the evolution equation, which is derived by regarding the deformation process of viscoelastic materials as an irreversible themodynamic process, depend very much on the properties of their coefficient matrices. These matrices are usually affected by the nature of the generalized thermodynamic coordinates, say, the number and location of the neutrally stable equilibrium coordinates and those participating in the entropy production of the isolated system. These provide us a ground to distinguish the ideal viscoelastic solid state and the ideal viscoelastic fluid state in creep or stress relaxation behaviour.