or end of certain intervals.  He does not concern himself with the interval in its actual duration.  This is proved by the fact that, could all velocities in the universe be doubled, the astronomical formulae would remain unaffected, for the coincidences with which that science deals would still take place, but at intervals half as long.  To the astronomer as such, this would make no difference, but we, in ourselves, would find that our day did not give us the full experience.  Situations which arose as a result of the introduction of “summer time” serve to make this point clear.  As then we find that time means two different things for the astronomer and the psychologist, the one being concerned with the points at the extremities of intervals, and the other with the enduring reality of the intervals themselves, we can see why astronomical phenomena are capable of prediction and see too that, for the same reason, events in the realm of human action cannot be so predicted and therefore the future is not predetermined but is being made.

Upon exactly parallel lines lie the references to causality in the controversy.  In the physical realm events may recur, but in the mental realm the same thing can never happen again because we are living in real, flowing time, or la duree, and our conscious states are changing.  Admitting that there is that in experience which warrants the application of the principle of causality, taking that principle as the statement that physical phenomena once perceived can recur, and that a given phenomenon, happening only after certain conditions, will recur when those precise conditions are repeated, [Footnote:  See the brief paper Notre croyance a la loi de causalite, Revue de metaphysique et de morale, 1900.] still it remains open whether such a regularity of succession is ever possible in the human consciousness, and so the assertion of the principle of causality proves nothing against Freedom.  We may admit that the principle is based on experience—­but what kind of experience?  Consideration of this question leads us to assert that the principle of causality only tends to accentuate the difference between objects in a realm wherein regular succession may be observed and predicted and a realm where it may not be observed or predicted, the realm of the self.  Just because I endure and change I do not necessarily act to-day as I acted yesterday, when under like conditions.  We do expect, however, that this will not be the case in the physical realm; for example, we expect that a flame applied to dry paper will always set it alight.  Indeed, the more we realize the causal relation as one of necessary determination, we come to see that things do not exist as we do ourselves, and distinction between physical and psychical events becomes clear.  We perceive that we, in ourselves, are centres of indetermination enjoying Freedom, and capable of creative activity.