not studied physics cannot be expected to perceive reasons that depend upon the laws of physics, and yet without a knowledge of physics he may still perceive that a statement is not of a mere fact, but of something that must have a reason. To primitive peoples nature was a closed book. The simplest phenomena were beyond their understanding, and they, therefore, imagined deities of whose personal activities these phenomena were supposed to be manifestations. With the progress of science many phenomena once mysterious and looked upon as facts have become easily explained. The intelligent student, however, can generally distinguish between statements of the different kinds which have been described, and he should constantly endeavor to explain or seek the reason for new statements by relating them to the body of knowledge which he has previously gained. Unfortunately, the average student reads only to accept what is written, whether fact, conclusion, or opinion, perhaps memorizing it verbatim under the impression that by so doing he is learning; he does not examine or reflect upon it, and often even accepts as facts what are explicitly stated to be mere expressions of opinion. Thus palpable mistakes, or even typographical errors, which a careful student should detect at once, are often accepted and believed. It is for this reason that it is so easy to deceive most people, at least for part of the time. They do not think for themselves, and all that is necessary to make them believe what you say is in some way to get them to think you are an authority.

(d) REGARDING FACTS WHICH HE DOES NOT THEN INVESTIGATE THE REASON FOR, HE SHOULD ASK How THEY ARE ASCERTAINED.—This will draw his attention to methods of observation and experiment, or to the technique of the subject. How, for instance, is it ascertained that New York is 90 miles from Philadelphia, or that the sun is ninety-two million miles from the earth? It is always possible to ascertain, at least in a general way, how a fact is ascertained, though it may not be possible to determine the reason for the fact. This applies not alone to physical sciences, but to questions of an economic, historic or sociological character. If we read that at the Battle of Gettysburg 3072 Union soldiers were killed, we do not inquire why; such a question is clearly meaningless; but we may well inquire how this was ascertained, whether by counting the dead upon the field or by the roll call, etc.; or if we read that following the issue of large quantities of paper currency during the Civil War, the amount of gold in the country decreased, we may in this case also inquire how it was ascertained, and we may further perceive that this is a fact for which there must be a reason, and we may then or later ascertain why it is true.

(e) THE STUDENT MUST TRAIN HIMSELF TO BE CONSTANTLY ON THE WATCH FOR EVIDENCE OF RELIABILITY IN THE WRITER HE IS STUDYING, IN ORDER THAT HE MAY GET A CORRECT IMPRESSION AS TO WHETHER HIS STATEMENTS OF FACT MAY BE ACCEPTED, AS WELL AS HIS CONCLUSIONS AND OPINIONS.—Many writers are careless, some are entirely unreliable, and some wilfully distort. Not only are the opinions sometimes expressed entirely unwarranted by the facts, but often statements of mere fact, such as those of statistics, may be grossly perverted, sometimes intentionally. Erroneous conclusions or opinions which are the result of illogical reasoning from correct facts may be discovered by the student who himself knows how to reason, but perversions of fact may escape detection, if not traced back to original authorities or observations, which the student may not have time or opportunity to do. Statistical results, or statements made in books on economics, history, and sociology, are particularly liable to distortion, intentionally or unintentionally. Indeed by selecting certain statistics and excluding others, almost anything depending upon statistics may be proved.

The importance is thus obvious of being able to detect signs of reliability and accuracy, and of discarding a writer who cannot be depended upon. It is also important to make it a rule to ask whether any result when reached appears to be reliable in the light of common sense. Sometimes a suggestion of error will be observed if the subject is looked at in this light, which if traced back will lead to the discovery of some mistake in observation or some error in reasoning.

Evidence of unreliability shown by a writer may generally be discovered, if care is exercised. His temperament, age, environment, training, religion and other facts will contribute. One who is dogmatic or abusive in stating what are obviously mere opinions which cannot be demonstrated, or who is intolerant of those who reach different conclusions, is obviously by temperament untrustworthy. A writer who in a single instance can be shown to have intentionally distorted facts should, of course, be at once and forever rejected;[2] one who has distorted facts unintentionally may perhaps be forgiven once. So a writer who, in a matter not capable of mathematical demonstration, and to some extent a matter of opinion, sets out to prove a preconceived idea, shows himself in general not possessed of the qualities which should inspire confidence.

By these and other tests the student should constantly be on the watch to form his opinion of the credibility and reliability of a writer or experimenter whose work he is studying. He may thus guide himself as to the books which he should pursue carefully, remembering the dictum of Bacon that "Some books are to be tasted, others to be swallowed, and some few to be chewed and digested," except that very few, if any, are to be literally swallowed without digestion. By careful observance of the injunction to study constantly the credibility of a writer one may become what may be termed a discriminating student.

(f) ANOTHER ESSENTIAL ELEMENT OF A PROPER ATTITUDE OF MIND IS CAUTION.—Always realize the possibility of error both in another and in yourself. Be on your guard against intentional or unintentional deception. As Bacon said, "Read not to contradict and to confute, nor to believe and take for granted, nor to find talk and discourse, but to weigh and consider."[3] The author you are reading may have made a mistake, or may be trying to mislead you. "When we think of the difficulty of finding the way, when we are most desirous to go right, how easy to mislead those whom we wish to go wrong!" Be, therefore, always suspicious of your author, and subject all his statements to the test of your own intelligence.[4]

(g) STUDY WITH AN OPEN MIND, AND WITH NO PRECONCEIVED IDEAS.—Cultivate the scientific attitude of mind, which means, first to formulate clearly a problem, then to get together all the pertinent facts, and then to draw the logical conclusions. Be ready to accept gladly any logical conclusion from the facts, even if unpalatable. Truth is, or should be, the sole object of study.[5]

(h) BE