'The notion that truths external to the mind,' he writes, 'may be known by intuition or consciousness, independently of observation and experience, is, I am persuaded, in these times, the great intellectual support of false doctrines and bad institutions. By the aid of this theory every inveterate belief and every intense feeling of which the origin is not remembered, is enabled to dispense with the obligation of justifying itself by reason, and is erected into its own all-sufficient voucher and justification. There never was an instrument better devised for consecrating all deep-seated prejudices. And the chief strength of this false philosophy in morals, politics, and religion, lies in the appeal which it is accustomed to make to the evidence of mathematics and of the cognate branches of physical science. To expel it from these is to drive it from its stronghold.... In attempting to clear up the real nature of the evidence of mathematical and physical truth, the _System of Logic_ met the intuitive philosophers on ground on which they had previously been deemed unassailable; and gave its own explanation from experience and association of that peculiar character of what are called necessary truths, which is adduced as proof that their evidence must come from a deeper source than experience. Whether this has been done effectually is still _sub judice_; and even then, to deprive a mode of thought so strongly rooted in human prejudices and partialities of its mere speculative support, goes but a very little way towards overcoming it; but though only a step, it is a quite indispensable one; for since, after all, prejudice can only be successfully combated by philosophy, no way can really be made against it permanently, until it has been shown not to have philosophy on its side' (pp. 225-227).