The theory of significance has been expanded and made more definite in the present volume. It had already been introduced in the _Principles of Natural Knowledge_ (cf. subarticles 3.3 to 3.8 and 16.1, 16.2, 19.4, and articles 20, 21). In reading over the proofs of the present volume, I come to the conclusion that in the light of this development my limitation of infinite events to durations is untenable. This limitation is stated in article 33 of the _Principles_ and at the beginning of Chapter IV (p. 74) of this book. There is not only a significance of the discerned events embracing the whole present duration, but there is a significance of a cogredient event involving its extension through a whole time-system backwards and forwards. In other words the essential 'beyond' in nature is a definite beyond in time as well as in space [cf. pp. 53, 194]. This follows from my whole thesis as to the assimilation of time and space and their origin in extension. It also has the same basis in the analysis of the character of our knowledge of nature. It follows from this admission that it is possible to define point-tracks [_i.e._ the points of timeless spaces] as abstractive elements. This is a great improvement as restoring the balance between moments and points. I still hold however to the statement in subarticle 35.4 of the _Principles_ that the intersection of a pair of non-parallel durations does not present itself to us as one event. This correction does not affect any of the subsequent reasoning in the two books. I may take this opportunity of pointing out that the 'stationary events' of article 57 of the _Principles_ are merely cogredient events got at from an abstract mathematical point of view. INDEX _In the case of terms of frequent occurrence, only those occurrences are indexed which are of peculiar importance for the elucidation of meaning._ A [_or_ an], 11 Abraham, 105 Absolute position, 105, 106, 114, 188 Abstraction, 33, 37, 168, 171, 173; extensive, 65, 79, 85 Abstractive element, 84; set, 61, 79 Action at a distance, 159, 190 Action by transmission, 159, 190 Active conditions, 158 Activity, field of, 170, 181 Adjunction, 101 Aggregate, 23 Alexander, Prof., viii Alexandria, 71 Alfred the Great, 137 Anticipation, 69 Anti-prime, 88 Apparent nature, 31, 39 Area, 99; momental, 103; vagrant, 103 Aristotelian logic, 150 Aristotle, 16, 17, 18, 24, 197 Associate-potential, 183 Atom, 17 Attribute, 21, 26, 150 Awareness, 3 Axiom, 36, 121 Axioms of congruence, 128 et seqq. Bacon, Francis, 78 Behaviouristic, 185 Bergson, 54 Berkeley, 28 Between, 64 Beyond, 186, 198 Bifurcation, vi, 30, 185, 187 Boundary, 100; moment, 63; particle, 100 Broad, C. D., viii Calculation, formula of, 45, 158 Cambridge, 97 Causal nature, 31, 39 Causation, 31, 146 Centrifugal force, 138 Change, uniformity of, 140