According to Kant, the reason of this property is found in the application to time of the principle of causality. As the parts of time, he says, are to each other in the relation of cause to effect, and as the cause is essentially antecedent to its effect, it is impossible to reverse this relation. According to the Scholastics, this immutability is based upon the very nature of concrete movement, of which one part is essentially anterior to another. Secondly, time is the measure of events in this world. This raises a knotty problem, which has so far not been theoretically solved.
Time can be a permanent measure only if it is concretized in a uniform movement.
Now, to know the uniformity of a movement, we must know not only the space traversed, but the velocity of the transit, that is the time. Here there is unquestionably a vicious circle. Lastly, for those who concretize time in movement, a much debated question is, whether time or movement can be infinite, that is without beginning. St. Thomas and some of the Scholastics see no absolute impossibility in this, but many modern thinkers take a different view. Remy Lafort, S.T.D., Censor Imprimatur.