In respect to these types of internal relationship between α and other occasions, these other occasions (as constitutive of α) can be classified in many alternative ways. These are all concerned with different definitions of past, present, and future. It has been usual in philosophy to assume that these various definitions must necessarily be equivalent. The present state of opinion in physical science conclusively shows that this assumption is without metaphysical justification, even though any such discrimination may be found to be unnecessary for physical science. This question has already been dealt with in the chapter on Relativity. But the physical theory of relativity touches only the fringe of the various theories which are metaphysically tenable. It is important for my argument to insist upon the unbounded freedom within which the actual is a unique categorical determination. Every actual occasion exhibits itself as a process: it is a becomingness. In so disclosing itself, it places itself as one among a multiplicity of other occasions, without which it could not be itself. It also defines itself as a particular individual achievement, focussing in its limited way an unbounded realm of eternal objects. Any one occasion α issues from other occasions which collectively form its _past_. It displays for itself other occasions which collectively form its _present_. It is in respect to its associated hierarchy, as displayed in this immediate present, that an occasion finds its own originality. It is that display which is its own contribution to the output of actuality. It may be conditioned, and even completely determined by the past from which it issues. But its display in the present under those conditions is what directly emerges from its prehensive activity. The occasion α also holds within itself an indetermination in the form of a future, which has partial determination by reason of its inclusion in α and also has determinate spatio-temporal relatedness to α and to actual occasions of the past from α and of the present for α. This future is a synthesis in α of eternal objects as not-being and as requiring the passage from α to other individualisations (with determinate spatio-temporal relations to α) in which not-being becomes being.