course, mean to intimate that we should have no opinions about matters that we have not personally investigated. We take, and ought to take, the opinion of some men about law, and others about medicine, and others about particular sciences, and so on. But we should clearly realize the difference between holding an opinion on trust and holding it as the result of our own investigations." Brooks says: "It should be one of the leading objects of the culture of young people to lead them to acquire the habit of forming judgments. They should not only be led to see things but to have opinions about things. They should be trained to see things in their relations and to put these relations into definite propositions. Their ideas of objects should be worked up into thoughts concerning the objects. Those methods of teaching are best which tend to excite a thoughtful habit of mind that notices the similitudes and diversities of objects and endeavors to read the thoughts which they embody and of which they are the symbols." The study of logic, geometry, and the natural sciences is recommended for exercise of the faculty of judgment and the development thereof. The study and practice of even the lower branches of mathematics are also helpful in this direction. The game of checkers or chess is recommended by many authorities. Some have advocated the practice of solving enigmas, problems, rebuses, etc., as giving exercise to this faculty of the mind. The cultivation of the "Why?" attitude of mind, and the answering of one's own mental questions, is also helpful, if not carried to excess. "Doubting Thomas" is not always a term of reproach in these days of scientific habits of thought, and "the man from Missouri" has many warm admirers. CHAPTER XXIV. Primary Laws of Thought. In connection with this subject we herewith call the attention of the student to the well-known Primary Laws of Thought which have been recognized as valid from the time of the ancient Greek logicians. These laws are self-evident, and are uncontradictable. They are axiomatic. Jevons says of them: "Students are seldom able to see at first their full meaning and importance. All arguments may be explained when these self-evident laws are granted; and it is not too much to say that the whole of logic will be plain to those who will constantly use these laws as their key." Here are the Three Primary Laws of Thought:-- I. _Law of Identity._ "Whatever is, _is_." II. _Law of Contradiction._ "Nothing can both be and not be." III. _Law of Excluded Middle._ "Everything must either be or not be; there is no middle course."