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114 preach because you have it." Errors, when useful to life, may in time become incorporated in the living organism and act as impulses there. Yet errors are errors, whatever their effect, whatever their beneficence. The question of the usefulness of an idea is separate from that of its truth. Not only does the agreeableness or comfort of an opinion prove nothing, its necessity to life proves nothing—among the conditions of life, error may be one.