rected to proving possibility, probability,
or actuality.

If we believe that an event actually occurred, the belief implies both
possibility and probability. Therefore, if we wish a person to believe in
the actual occurrence of an event, we must first be sure that he does not
question the possibility of its existence, and then we must show him that
it probably did take place. Only when we have shown that an event is
extremely probable have we the right to say that we have shown its actual
occurrence.

A mother finding some damage done to one of the pictures on the wall could
not justly accuse her young son unless by the presence of a chair or
stepladder it had been possible for him to reach the picture. This
possibility, reenforced by a knowledge of his tendency to mischief, and by
the fact that he was in the house at the time the damage was done, would
lead to the belief that he probably was guilty. Proof that he was actually
responsible for the damage would still be lacking, and it might later be
discovered that the injury had been done accidentally by one of the
servants.

Possibility, probability, and actuality merge into one another so
gradually that no sharply defined distinctions can be observed. It is
impossible to say that a certain argument establishes possibility, another
probability, and a third the actuality of an event. One statement may do
all three, but any proof of actuality must include arguments showing both
possibility and probability. A person accused of murder attempts to
demonstrate his innocence by proving an _alibi;_ that is, he attempts to
show that he was at some other place at the time the murder was committed
and so cannot possibly be guilty. Such an alibi, established by reliable
witnesses, is positive proof of innocence, no matter how strong the
evidence pointing to probable guilt may be.

+189. Argument from Cause.+--We have learned, in Section 49, that the
relation of cause and effect is one which is ingrained in our nature. We
accept a proposition as plausible if a cause which we consider adequate
has been assigned. Our belief in a proposition often depends upon our
belief in some other proposition which may be accepted as a cause.

Thus, in the following statements, the truth of one proposition leads to
the belief that the other is also true:--

_a._ Henry has studied hard this year; therefore he will pass his college
entrance examinations.

_b._ The man has severed an arter