One of the most marked features about the law of mind is that it makes
time to have a definite direction of flow from past to future. The
relation of past to future is, in reference to the law of mind, different
from the relation of future to past. This makes one of the great
contrasts between the law of mind and the law of physical force, where
there is no more distinction between the two opposite directions in time
than between moving northward and moving southward.
In order, therefore, to analyse the law of mind, we must begin by asking
what the flow of time consists in. Now, we find that in reference to any
individual state of feeling, all others are of two classes, those which
affect this one (or have a tendency to affect it, and what this means we
shall inquire shortly), and those which do not. The present is affectible
by the past but not by the future.
Moreover, if state _A_ is affected by state _B_, and state _B_ by state
_C_, then _A_ is affected by state _C_, though not so much so. It
follows, that if _A_ is affectible by _B_, _B_ is not affectible by _A_.
If, of two states, each is absolutely unaffectible by the other, they are
to be regarded as parts of the same state. They are contemporaneous.
To say that a state is _between_ two states means that it affects one
and is affected by the other. Between any two states in this sense lies
an innumerable series of states affecting one another; and if a state
lies between a given state and any other state which can be reached by
inserting states between this state and any third state, these inserted
states not immediately affecting or being affected by either, then the
second state mentioned immediately affects or is affected by the first,
in the sense that in the one the other is _ipso facto_ present in a
reduced degree.
These propositions involve a definition of time and of its flow. Over and
above this definition they involve a doctrine, namely, that every state
of feeling is affectible by every earlier state.