These considerations carry us, of course, right into what is perhaps the most fundamental of all metaphysical problems: that of the mode in which finite reality is actual. In its concrete actuality every finite real being is essentially subject to change: its actuality is not _tota simul_: at every instant it not only _is_ but is _becoming_: it is a mixture of potentiality and actuality: it is ever really changing, and yet the “it” which changes can in some real degree and for some real space of time persist or endure identical with itself as a “subsisting thing” or “person”. How, then, are we to conceive aright the mode of its actuality? Take the concrete existing being at any instant of its actuality: suppose that it is not merely undergoing change through the influence of other beings in its environment, or through its own immanent action, but that it is itself “acting,” whether immanently or transitively. If we consider that at this instant its _existence_ is “really distinct” from its _action_ we cannot mean by this that there is in it an unchanging substantial core, which is actually merely “existing,” and a vesture of active and passive accidental principles, which is just now actual (though always in a state of flux or change) by “acting” or “being acted on”.(345) Such a conception would conflict with the truth that the existing substance is ever being really and actually, though accidentally, determined, changed, modified, improved or disimproved, in its total concrete existing reality. Even when these changes are not so profound as to destroy its substantial identity and thus terminate its actuality as an individual being, even when, in other words, they are not substantial, they are none the less real and really affect the substance. Since they are real they necessarily involve the recognition of really distinct principles in the concrete being and preclude the view that the distinctions which we recognize in the ever-changing modes of its actuality, as revealed to us in time and space, are all _merely_ conceptual or logical distinctions projected by the mind into what would therefore be in fact a simple and immutable reality. The denial of any real distinction between successive actual states, or between co-existing principles of those states, in any finite being, would lead logically to the Eleatic doctrine, _i.e._ to denial of the reality of change. On the other hand, while recognizing that change is a reality and not a subjective mental illusion, and that real change can be grounded only in a plurality of really distinct principles in the finite individual being, we must at the same time hold that this plurality of really distinct principles in the individual does not destroy a real unity, stability, and self-identical continuity of the individual being