Kinematic quantities for finite elastic and plastic deformations are defined via an approach that does not rely on auxiliary elements, such as reference frame and reference configuration, and that gives account of the inertial–noninertial aspects explicitly. These features are achieved by working on Galilean spacetime directly. The quantity expressing elastic deformations is introduced according to its expected role: to measure how different the current metric is from the relaxed/stressless metric. Further, the plastic kinematic quantity is the change rate of the stressless metric. The properties of both are analyzed, and their relationship with frequently used elastic and plastic kinematic quantities is discussed. One important result is that no objective elastic or plastic quantities can be defined from the deformation gradient. Copyright © 2012 John Wiley & Sons, Ltd.