Measuring time is expressing temporal relationships between objects in terms of spatial relationships with the aid of geometric points, straight lines and clocks. The concepts, point and line, are abstracted from the concrete substratum of sensory experience. This process of abstraction is integrated with the psychological processes which go on within an observer who is reading a clock. The analysis of clock-reading from a psychological point of view points up the necessity to differentiate between two modalities of time: objective time, or, time relationships between objects and which can be expressed in terms of space with point, line and clock; and subjective time, or, the time structure of the human individual in which region point and line are irrelevant concepts. From this irrelevance of point and line it follows that subjective time cannot be measured.