"there is a class of persons (happily not quite so numerous as formerly) who think it enough if a person assents undoubtingly to what they think true, though he has no knowledge whatever of the grounds of the opinion, and could not make a tenable defence of it against the most superficial objections. such persons, if they can once get their creed taught from authority, naturally think that no good, and some harm, comes of its being allowed to be questioned. where their influence prevails, they make it nearly impossible for the received opinion to be rejected wisely and considerately, though it may still be rejected rashly and ignorantly; for to shut out discussion entirely is seldom possible, and when it once gets in, beliefs not grounded on conviction are apt to give way before the slightest semblance of an argument. waiving, however, this possibility — assuming that the true opinion abides in the mind, but abides as a prejudice, a belief independent of, and proof against, argument — this is not the way in which truth ought to be held by a rational being. this is not knowing the truth. truth, thus held, is but one superstition the more, accidentally clinging to the words which enunciate a truth."explain?