For even if we consider two ultimate instants and two ultimate points, the difference between them in each case being smaller than any given quantity, and their differentiation being at an incipient stage, the idea of a moving body identical throughout the phases of motion excludes, as a mere appearance, the phenomenon of 'shift', and implies the idea of a spatial and temporal position always identifiable in itself, even if it is not so for us, and therefore that of a stone which always is and never changes.