. This is not an idea merely that
intellectual error is a pathological necessity of the mind, no more to
be escaped than the pathological necessities which afflict and finally
dissolve the body. That is historically true. It is an idea that error
somehow in certain stages, where there is enough of it, actually does
good, like vaccination. Well, the thesis of the present chapter is that
erroneous opinion or belief, in itself and as such, can never be useful.
This may seem a truism which everybody is willing to accept without
demur. But it is one of those truisms which persons habitually forget
and repudiate in practice, just because they have never made it real to
themselves by considering and answering the objections that may be
brought against it. We see this repudiation before our eyes every day.
Thus for instance, parents theoretically take it for granted that error
cannot be useful, while they are teaching or allowing others to teach
their children what they, the parents, believe to be untrue. Thus
husbands who think the common theology baseless and unmeaning, are found
to prefer that their wives shall not question this theology nor neglect
its rites. These are only two out of a hundred examples of the daily
admission that error may be very useful to other people. I need hardly
say that to deny this, as the commonplace to which this chapter is
devoted denies it, is a different thing from denying the expediency of
letting errors alone at a given time. That is another question, to be
discussed afterwards. You may have a thoroughly vicious and dangerous
enemy, and yet it may be expedient to choose your own hour and occasion
for attacking him. 'The passage from error to truth,' in the words of
Condorcet, 'may be accompanied by certain evils. Every great change
necessarily brings some of these in its train; and though they may be
always far below the evil you are for destroying, yet it ought to do
what is possible to diminish them. It is not enough to do good; one must
do it in a good way. No doubt we should destroy all errors, but as it is
impossible to destroy them all in an instant, we should imitate a
prudent architect who, when obliged to destroy a building, and knowing
how its parts are united together, sets about its demolition in such a
way as to prevent its fall from being dangerous.'[8]

Those, let us note by the way, who are accustomed to think the moral
tone of the eighteenth century low and gross compared wit