ON THE UNCERTAINTY OF CONCLUSIONS. 
17 
subject in hand, a single example of this method of treatment 
may be useful: 
Let there be two witnesses, A and B. Suppose that A tells 
the truth 51 times out of 100—that is to say, assume that 
honesty holds the controlling share in his stock of moral 
principles. Let B be equally truthful and no more. Then 
if these two testify independently to the occurrence of a cer¬ 
tain phenomenon it is more likely to have occurred than if 
either one alone bore witness. This is evidence in parallel. 
If, however, A testifies that B declares that the thing hap¬ 
pened, it is less probable than if based on the testimony of 
either alone. This is evidence in series. Put as boldly as 
this, no one doubts the higher value of the first arrangement; 
but it is believed that a more careful consideration of this 
distinction will do much to secure a better judgment, not 
only where human testimony is involved, for here it has 
long been an established principle, but where conclusions 
are based on observation and experiment. 
It is of the utmost importance, therefore, that men of science, 
before accepting a theory or a hypothesis as final, should 
carefully scrutinize the steps by which it has been estab¬ 
lished to see that they are not only sufficient but necessary. 
The true philosopher will be slow to claim that the theory 
which he finds sufficient to explain all of a given class of 
facts is the necessary and true one; he will be constantly on 
the lookout for a new fact which his theory will not quite 
explain, and he will have much consideration for his friendly 
competitor who finds a different hypothesis equally satis¬ 
factory and efficient. Above all, he will not pride himself 
on the steadfastness of his views and will rarely bind him¬ 
self to be of the same opinion this year as last. 
If the general public could be made to understand the 
limitations by which science is circumscribed, the tentative 
and ever progressive character of scientific investigation, it 
would be good for the public and good for science. 
The human race is greatly handicapped by the presence 
of a good number of people who strenuously object to being 
3—Bull. Phil. Soc., Wash., Vol, 12. 
