The concept that the lithosphere behaves as a perfectly rigid body during plate tectonism is challenged as a fundamental rule in the theory of new global tectonics. Experimental studies in rock mechanics indicate that confining pressure, temperature, solutions, the size of masses, and strain rate produce plates of little fundamental strength which can be subjected to plastic deformation by conventional geologic processes. A plastic plate tectonics model is geologically more realistic than the rigid body concept. The rigid model is believed to place some confining and perhaps unnecessary restrictions on the theory of global tectonics. The plastic plate model allows new possibilities concerning the fit of continental masses, as well as new interpretations related to the change in shape of such plates as they are transported across the surface of the Earth.