tions are
concerned solely with events, and exclusion is capable of logical
definition in terms of inclusion.

[10] Cf. note on 'significance,' pp. 197, 198.

[11] Cf. Ch. III, pp. 51 et seq.

Perhaps the most obvious exhibition of significance is to be found in
our knowledge of the geometrical character of events inside an opaque
material object. For example we know that an opaque sphere has a centre.
This knowledge has nothing to do with the material; the sphere may be a
solid uniform billiard ball or a hollow lawn-tennis ball. Such knowledge
is essentially the product of significance, since the general character
of the external discriminated events has informed us that there are
events within the sphere and has also informed us of their geometrical
structure.

Some criticisms on 'The Principles of Natural Knowledge' show that
difficulty has been found in apprehending durations as real
stratifications of nature. I think that this hesitation arises from the
unconscious influence of the vicious principle of bifurcation, so deeply
embedded in modern philosophical thought. We observe nature as extended
in an immediate present which is simultaneous but not instantaneous, and
therefore the whole which is immediately discerned or signified as an
inter-related system forms a stratification of nature which is a
physical fact. This conclusion immediately follows unless we admit
bifurcation in the form of the principle of psychic additions, here
rejected.

Our 'percipient event' is that event included in our observational
present which we distinguish as being in some peculiar way our
standpoint for perception. It is roughly speaking that event which is
our bodily life within the present duration. The theory of perception
as evolved by medical psychology is based on significance. The distant
situation of a perceived object is merely known to us as signified by
our bodily state, _i.e._ by our percipient event. In fact perception
requires sense-awareness of the significations of our percipient event
together with sense-awareness of a peculiar relation (situation) between
certain objects and the events thus signified. Our percipient event is
saved by being the whole of nature by this fact of its significations.
This is the meaning of calling the percipient event our standpoint for
perception. The course of a ray of light is only derivatively connected
with perception. What we do perceive are objects as related to events
signi