In a work of this nature, surveying so wide and difficult a field, no doubt errors will be detected; some oversight of matters worthy of attention, some instances of bad reasoning, and of that laxity of phrase against which it is so difficult to guard. Such errors I shall rejoice to see corrected, being anxious only for the fullest investigation of the subject, for the advancement of mental and moral science. My wish is to be one of those combatants whom Locke describes as a champion for knowledge, truth, and peace; not a slave to vainglory, ambition, or a party.