We find that under given conditions our measurements are necessarily made in some one pair which together form our natural measure-system.

The difficulty as to discordant time-systems is partly solved by distinguishing between what I call the creative advance of nature, which is not properly serial at all, and any one time series.

We habitually muddle together this creative advance, which we experience and know as the perpetual transition of nature into novelty, with the single-time series which we naturally employ for measurement.

The various time-series each measure some aspect of the creative advance, and the whole bundle of them express all the properties of this advance which are measurable.

The reason why we have not previously noted this difference of time-series is the very small difference of properties between any two such series.