hat no other kind of rationality than this exists. The daily
contemplation of phenomena juxtaposed in a certain order begets an
acceptance of their connection, as absolute as the repose engendered by
theoretic insight into their coherence. To explain a thing is to pass
easily back to its antecedents; to know it is easily to foresee its
consequents. Custom, which lets us do both, is thus the source of
whatever rationality the thing may gain in our thought.

In the broad sense in which rationality was defined at the outset of
this essay, it is perfectly apparent that custom must be one of its
factors. We said that any perfectly fluent and easy thought was devoid
of the sentiment of irrationality. Inasmuch then as custom acquaints
us with all the relations of a thing, it teaches us to pass fluently
from that thing to others, and _pro tanto_ tinges it with the rational
character.

Now, there is one particular relation of greater practical importance
than all the rest,--I mean the relation of a thing to its future
consequences. So long as an object is unusual, our expectations are
baffled; they are fully determined as soon as it becomes familiar. I
therefore propose this as the first practical requisite which a
philosophic conception must satisfy: _It must, in a general way at
least, banish uncertainty from the future_. The permanent presence of
the sense of futurity in the mind has been strangely ignored by most
writers, but the fact is that our consciousness at a given moment is
never free from the ingredient of expectancy. Every one knows how when
a painful thing has to be undergone in the {78} near future, the vague
feeling that it is impending penetrates all our thought with uneasiness
and subtly vitiates our mood even when it does not control our
attention; it keeps us from being at rest, at home in the given
present. The same is true when a great happiness awaits us. But when
the future is neutral and perfectly certain, 'we do not mind it,' as we
say, but give an undisturbed attention to the actual. Let now this
haunting sense of futurity be thrown off its bearings or left without
an object, and immediately uneasiness takes possession of the mind.
But in every novel or unclassified experience this is just what occurs;
we do not know what will come next; and novelty _per se_ becomes a
mental irritant, while custom _per se_ is a mental sedative, merely
because the one baffles while the other settles our exp