Note 5 — Chapter II

The idea that time may be an active factor in causation has the mathematical significance that ‘t’ (for the system in question) must appear explicitly in the formulation of the law, and not merely as the square of a time-differential found convenient for the correlation of a standard clock with a reversible process which is being observed. A law whose mathematical formulation involves ‘t’ measured from some moment in the history of the system, gives an entirely new meaning to ‘t’, though one consistent with the properties of the reversible Newtonian differential ‘dt’. Such a law may claim to express the fact of historic, irreversible, duration, a feature in nature which is neglected by laws involving only ‘dt’ squared.