be informed of the classes which they should have in mind by the question, "What relationship exists between angles formed when parallel lines are cut by a transversal?" Finally, if more assistance were needed, the consequences could be suggested by asking, "In the case of figure I what relation exists between 1 and 4? between 3 and 5? What is the sum of 24+22+<5?”

Thus fertility of suggestion may be stimulated by the teacher's getting students to analyze, or break up, a problem or situation into various aspects, to formulate various hypotheses or guessed solutions of the problem, and to recall and apply certain general principles which they have in stock.

III. Critical Evaluation of Suggestions

So far we have discussed two aspects of reflective thinking, namely (I) defining the problem and keeping it in mind, and (II) fertility of suggestion. The third aspect to be considered is the critical, unbiased evaluation of suggestions from the standpoint of their bearing on the problem.

Critical ability may offset mediocre fertility of suggestion. This aspect may be contrasted with the second aspect which we discussed, namely, fertility of suggestion. Such fertility is valuable only when it is correlated with the other two factors, namely, clear realization of the problem and critical selection and rejection with reference to it. Here again we find interesting individual differences. A person possessed of much knowledge and ready recall may be an inefficient thinker because he lacks critical ability or critical habits. Hence the child who may be considered bright when measured by the standard of glib suggestions may be stupid when measured by the standard of critical, controlled thinking. On the other hand, a person may be only mediocre in knowledge and readiness of recall but be a fairly efficient thinker because of superior critical ability.

Expressed as aspects of the teacher's method, the discussion of unbiased critical evaluation of suggestions may be formulated as follows :

1. Maintain attitude of suspended judgment. — The teacher should encourage pupils to maintain an attitude of suspended conclusion or suspended judgment. This is necessary not only in order to provide for a thorough canvass of the problem but also in order to obviate bias which may interfere with the thinker's selection and evaluation of data or evidence. As Dewey says in the quotation given above (page 184), "the most important factor in the training of good mental habits consists in acquiring the attitude of suspended conclusion."

Discussing the matter further, he says:

Imagine a doctor called in to prescribe for a patient. The patient tells him some things that are wrong; his experienced eye, at a glance, takes in other signs of a certain disease. But if he permits the suggestion of this special disease to take possession prematurely of his mind, to become an accepted conclusion,his scientific thinking is by that much cut short. A large part of his technique as a practitioner is to prevent the acceptance of the first suggestions that arise. (5: 74)

The maintenance of the attitude of suspended conclusion, however, does not mean that the student will refrain from formulating definite hypotheses, but it means that he will evaluate these hypotheses in an open-minded and unbiased way. This brings us to the next phase of the teacher's method of training in reflective thinking.

2. Criticize all suggestions. — The teacher will stimulate students to criticize each suggestion and to think out its possible consequences. This process is discussed by Dewey in the following terms:

Acceptance of the suggestion in its first form is prevented by looking into it more thoroughly. Conjectures that seem plausible

at first sight are often found unfit or even absurd when their full consequences are traced out. Even when reasoning out the bearings of a supposition does not lead to rejection, it develops the idea into a form in which it is more apposite to the problem. . . . Suggestions at first seemingly remote and wild are frequently so transformed by being elaborated into what follows from them as to become apt and fruitful. (5: 76)

This idea is so well illustrated by the long quotation concerning the investigations by Kepler, given above on page 180, that further examples are unnecessary.

3. Be systematic in selecting and rejecting hypotheses. The teacher will stimulate students to be systematic in selecting useful suggestions and rejecting useless ones. The emphasis here is on orderliness in selection and rejection. Critical evaluation will proceed much more economically if it can be so ordered as to avoid useless repetition. Hence the alternative suggestions or hypotheses which present themselves may be arranged in some order, and then considered in turn, each one being followed through in a careful and fairly thorough way. This simply means that the rule about keeping the problem clearly in mind is applied to the consideration of the various subproblems into which the main problem becomes resolved. An unskilled thinker will jump around in a more or less haphazard way from one hypothesis to another. In this way he goes over the same ground time and again and works around in a circle to a considerable extent. Again, illustrations of this failure in reflective thinking are found in the deliberations of legislative bodies, committees, etc. The chairman is constantly under the necessity of reminding some member that the topic or suggestion which he is discussing has already been thrashed out in the previous discussion and that now the meeting is considering some other aspect of the case.

This emphasis on the systematic checking and following through of one aspect at a time does not mean, however,

that the thinker should refrain from returning to reconsider any hypothesis, provided some new evidence or implication occurs to mind; but he ought to realize clearly at the time that it is new evidence or implication. Even in this case it may often be well to note the necessity of returning for reëxamination of the previous hypothesis but to continue at the time the consideration of the aspect to which attention was being devoted at the time the evidence for reconsideration came to mind.

4. Verify by further evidence and by testing influences. The teacher should stimulate students to verify their conclusions. One method of doing this is simply to examine other cases to see if the conclusion holds for them also. Thus, when a college president endeavors to prove the superior value of a college education by pointing to the number of college graduates who have attained high office, the unbiased investigator will ask for further evidence in the form of a random selection of college graduates, which will be found to contain men in all walks of life, including tramps and other undesirable citizens. Or if a high-school principal is claiming that he has a superior school because some of his graduates have won honors in college, verification may be secured by investigating the records of all of his graduates that go to college from several classes.

Example of Newton's verification of law of universal gravitation. Another method of verification is to infer from the conclusion or proposition that certain other results must follow if it is true, and then to test to see if they do follow in point of fact. For example, Sir Isaac Newton (1642-1727) desired to test his conclusion that all bodies attract each other directly as their masses and inversely as the square of the distance between them, that is, the law of universal gravitation. He chose the attraction between the earth and the moon as a basis for verification, and compared the inferred movements of the moon according to his law with its actual movements as observed by astronomers. He

knew from actual astronomical observations and calculations that the moon was deflected from its tangent thirteen feet a minute; but by the calculation which he made in 1666, if the moon were deflected by gravity, according to his law it should be deflected fifteen feet a minute. So he decided that his hypothesis was not proved, because it did not agree with the observed astronomical facts. In time, however, it was discovered that the magnitude of the radius of the earth which he had used in his calculation of 1666 was incorrect. In 1679, using the correct magnitude, he repeated the calculation of the deflection of the moon according to his law, and found that the result agreed with the observed facts and consequently verified his hypothesis.

Two methods of verification illustrated by debate concerning heredity and environment. Both methods of verification may be illustrated by the debate concerning the relative influence of environment and heredity or original nature. One person may make the statement that he believes heredity is not an important factor, because he knows of a particular case in which a son's traits could not be derived from his parents. Verification in this particular case might involve getting further evidence about it—further family history which might show, for example, that the son was like his grandfather and thus establish the fact of heredity.

The other method of verification might start from the following statement: "If heredity or original nature is a very powerful factor, we may infer that similar children who are brought up under different circumstances ought to remain similar, and different (dissimilar) children who are brought up under identical circumstances ought to remain different (dissimilar)." The verification would consist in finding such cases and noting the actual results, as Sir Francis Galton did in England in the case of similar twins brought up under different circumstances, and dissimilar twins brought up under similar circumstances. The evidence was strongly in favor of