McTaggart argues that the conception of time as only forming a B-series is inadequate because the B-series does not change, and change is of the essence of time. If any conception of reality represents it as changeless, then this is a conception of an atemporal reality. The B-series does not change because earlier-later relationships never change (e.g. the year 2010 is always later than 2000). The events that form a B-series must therefore also form an A-series in order to count as being in time, i.e. they must pass from future to present, and from present to past, in order to change.