And since in this series of aggregated spaces of a given space (e.g., the feet in a rod), the further spaces, starting with a given one, are each thought of as the condition of the boundaries of the previous ones, the measurement of a space is to be regarded as a synthesis of a series of conditions for a given conditioned; only the side of the conditions is not in itself distinguished from the side lying beyond the conditioned, consequently regressus and progressus in space appear to be one and the same.