There is a category of objects such that for any two occurrences of an object in that category, Establishing the highest degree of their qualitative identity will not be sufficient to establish that the object involved is one and the same. It is first argued that objects in this category occupy positions in a spatio-Temporal continuum and obey certain principles of conservation. And then two criteria for the numerical identity of these objects are developed: (a) that there are scientific laws (...) which can, In principle, Predict or retrodict a continuous path for the object; (b) that the parts of the object and their arrangement are preserved in a certain specified way. (shrink)