vents for the ingression as thus limited. The percipient
event is the relevant bodily state of the observer. The situation is
where he sees the blue, say, behind the mirror. The active conditioning
events are the events whose characters are particularly relevant for the
event (which is the situation) to be the situation for that percipient
event, namely the coat, the mirror, and the state of the room as to
light and atmosphere. The passive conditioning events are the events of
the rest of nature.

In general the situation is an active conditioning event; namely the
coat itself, when there is no mirror or other such contrivance to
produce abnormal effects. But the example of the mirror shows us that
the situation may be one of the passive conditioning events. We are then
apt to say that our senses have been cheated, because we demand as a
right that the situation should be an active condition in the
ingression.

This demand is not so baseless as it may seem when presented as I have
put it. All we know of the characters of the events of nature is based
on the analysis of the relations of situations to percipient events. If
situations were not in general active conditions, this analysis would
tell us nothing. Nature would be an unfathomable enigma to us and there
could be no science. Accordingly the incipient discontent when a
situation is found to be a passive condition is in a sense justifiable;
because if that sort of thing went on too often, the _role_ of the
intellect would be ended.

Furthermore the mirror is itself the situation of other sense-objects
either for the same observer with the same percipient event, or for
other observers with other percipient events. Thus the fact that an
event is a situation in the ingression of one set of sense-objects into
nature is presumptive evidence that that event is an active condition in
the ingression of other sense-objects into nature which may have other
situations.

This is a fundamental principle of science which it has derived from
common sense.

I now turn to perceptual objects. When we look at the coat, we do not in
general say, There is a patch of Cambridge blue; what naturally occurs
to us is, There is a coat. Also the judgment that what we have seen is
a garment of man's attire is a detail. What we perceive is an object
other than a mere sense-object. It is not a mere patch of colour, but
something more; and it is that something more which we judge to be a
co