Matter as it appears to common sense, and as it has until recently appeared in physics, must be given up. The old idea of matter was connected with the idea of “substance”, and this, in turn, with a view of time that the theory of relativity shows to be untenable. The old view was that there is one cosmic time, and that, given any two events in any two parts of the universe, either they are simultaneous, or the first is earlier than the second, or the second earlier than the first. It was thought that the time-order of the two events must always be objectively definite, although _we_ might be unable to determine it. We now find that this is not the case. Events which can be regarded as all in one place, or all parts of the history of one piece of matter, still have a definite time-order. So do events in different places if a person situated where the second takes place can see the first before the second happens, or, more exactly, if light can travel from the place of the one to the place of the other so as to reach the other place before the second event. (Here we mean by a “place” the position of a given piece of matter: however the matter may move relatively to other matter, it is always in the same “place” from its own point of view.) But if light travelling from the place of the one event to the place of the other event arrives at the place of the other event after the other event has taken place, and conversely, then there is no definite objective time-order of the two events, and there is no reason for regarding either as earlier than the other; nor yet for regarding the two as simultaneous; ideally careful observers will judge differently according to the way in which they are moving. Thus time is not cosmic, but is to some extent individual and personal for each piece of matter.