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 artery; therefore he will probably bleed to death before the physician arrives.

c. It will soon grow warmer, because the sun has risen.

An argument from cause may be of itself conclusive evidence of the fact.  But, for the most part, such arguments merely establish the possibility or probability of the proposition and so render it ready for proof.  In our arrangement of material, we therefore place such arguments first.