That a special preparation of mind is required for each separate department of inquiry and discussion (excepting, of course, that of abstract science) is strongly insisted upon in well-known passages of the Nicomachean Ethics. Speaking of the variations which are found in the logical perfection of proof in various subject-matters, Aristotle says, “A well-educated man will expect exactness in every class of subjects, according as the nature of the thing admits; for it is much the same mistake to put up with a mathematician using probabilities, and to require demonstration of an orator. Each man judges skilfully in those things about which he is well-informed; it is of these, that he is a good judge; viz. he, in each subject-matter, is a judge, who is well-educated in that subject-matter, and he is in an absolute sense a judge, who is in all of them well-educated.” Again: “Young men come to be mathematicians and the like, but they cannot possess practical judgment; for this talent is employed upon individual facts, and these are learned only by experience; and a youth has not experience, for experience is only gained by a course of years. And so, again, it would appear that a boy may be a mathematician, but not a philosopher, or learned in physics, and for this reason,—because the one study deals with abstractions, while the other studies gain their principles from experience, and in the latter subjects youths do not give assent, but make assertions, but in the former they know what it is that they are handling.” These words of a heathen philosopher, laying down broad principles about all knowledge, express a general rule, which in Scripture is applied authoritatively to the case of revealed knowledge in particular;—and that not once or twice only, but continually, as is notorious. For instance:—“I have understood,” says the Psalmist, “more than all my teachers, because Thy testimonies are my meditation.” And so our Lord: “He that hath ears, let him hear.” “If any man will do His will, he shall know of the doctrine.” And “He that is of God, heareth the words of God.” Thus too the Angels at the Nativity announce “Peace to men of good will.” And we read in the Acts of the Apostles of “Lydia, whose heart the Lord opened to attend to those things which were said by Paul.” And we are told on another occasion, that “as many as were ordained,” or disposed by God, “to life everlasting, believed.” And St. John tells us, “He that knoweth God, heareth us; he that is not of God, heareth us not; by this we know the spirit of truth, and the spirit of error.” 1.