Our minds are immediately aware of a ``flight of time'' without the intervention of external senses. Presumably there are more or less cyclic processes occurring in the brain, which play the part of a material clock, whose indications the mind can read. The rough measures of duration made by the internal time-sense are of little use for scientific purposes, and physics is accustomed to base time-reckoning on more precise external mechanisms. It is, however, desirable to examine the relation of this more primitive notion of time to the scheme developed in physics. Much confusion has arisen from a failure to realise that time as currently used in physics and astronomy deviates widely from the time recognised by the primitive time-sense. In fact the time of which we are immediately conscious is not in general physical time, but the more fundamental quantity which we have called interval (confined, however, to timelike intervals). \PageSep{24} Our time-sense is not concerned with events outside our brains; it relates only to the linear chain of events along our own track through the world. We may learn from another observer similar information as to the time-succession of events along his track. Further we have inanimate observers---clocks---from which we may obtain similar information as to their local time-successions. The combination of these linear successions along different tracks into a complete ordering of the events in relation to one another is a problem that requires careful analysis, and is not correctly solved by the haphazard intuitions of pre-relativity physics. Recognising that both clocks and time-sense measure~$ds$ between pairs of events along their respective tracks, we see that the problem reduces to that which we have already been studying, viz.\ to pass from a description in terms of intervals between pairs of events to a description in terms of coordinates.