is necessary for him to employ the work of
others, submitting, from time to time such accepted work to the tests
suggested by his own observations. He learns to regard in a different
light all knowledge taken on the authority of others; to distrust it a
little until he has learned to weigh its general credibility by his
own standards, and its particular credibility by subjecting portions
of it to his own tests; to distrust it still more when even small
portions fail to answer his tests, and to reject it altogether when
the percentage of detected error is large. He learns, in fact, what
Huxley called the duty of doubt.

This duty has not been universally accepted. In the history of
Christian civilisation (and a parallel series of events might be
portrayed from the history of other civilisations), many great
institutions and very many great and good men have condemned and
feared the habit and attitude of doubt in all its forms. Certain
doctrines believed to be of supreme importance to mankind were held to
rest on authority independent of, and perhaps not susceptible to, the
kind of testing employed in science. Around these doctrines there
grew, in time, a body of traditions, customs, new dogmas, and
fantasies; and the duty of belief in the first was extended to cover
the whole system, the central jewel as well as the accretions and
encrustations of time. The domain of religious authority was extended
to the whole field of human thought and of human action, and the more
unreasonable the dominion became, the more strenuously was the duty of
belief urged. The Protestant Reformation was one of the great stages
in the conflict for freedom against the universal tyranny that had
arisen, but the reformers very naturally retained a considerable
portion of the bias against which they had fought. In Protestant
countries, in the first half of this century, the duty of belief in
the Protestant doctrines, traditions, philosophy, history, and
attitude to science reigned supreme, and all weapons, from legitimate
argument to abusive invective and social ostracism, were employed
against those who acted in accordance with the duty of doubt.
Allegations of "unsoundness" or of "free thinking" became barriers to
success in life, and those against whom they were made became lowered
in the esteem of their fellows.

At the present time, when the advance of science and of civilisation
has almost won the battle for freedom of thought, it is diff