Summary: We present a conceptual framework to test different viscoelastic constitutive laws. This framework has the advantage of satisfying a priori thermodynamic restrictions, and is valid for large deformations. In addition, different mechanical contributions are separated according to time scales of their effects. As an illustration of its ability to model the immediate-time memory, short-time memory and long-time memory contributions the framework is used to identify mechanical tests performed on human patellar tendons. The resulting viscoelastlc law is then proposed to model soft biological tissues as these tissues exhibit an important viscoelastic behaviour.