Iron may, further, be changed by contact with other substances than air so as to lose its properties. Strong vinegar, which contains the substance known to chemists as acetic acid, acts upon iron, causing it to lose its characteristic properties. Changes of this kind, in which the substances disappear and something else is formed in their place, are known as chemical changes. Physical changes. There are many changes taking place which do not affect the composition of substances. Iron, for example, may be changed in many ways and still remain iron. It may become hotter or colder. .. (20: 1-2) Method based on common characteristics of familiar examples. These two examples quoted above furnish us with two typical methods of teaching the meaning of new abstract or general terms. The first quotation is itself phrased entirely in general terms and gives no familiar examples. The second quotation, on the other hand, (1) begins with familiar examples, (2) uses them to bring out a common characteristic (namely, a certain type of change in substances), and (3) provides at the end of the process the technical term chemical changes as a means of designating, thinking about, and talking about the characteristic aspect of the situation which has been under discussion. Example of exercises to test grasp of meaning.— Another type of procedure in teaching the meaning of abstract or general terms is to give a preliminary discussion consisting of a few familiar examples, with a statement of the definition, and then to provide a number of exercises in thinking, which are expected to be effective in making the meaning clear. This procedure is illustrated by the following quotation from a textbook on psychology, although no definition is given in this case. I. Mental Facts The world is made up of physical and mental facts. On the one hand there are solids, liquids, and gases, plants, trees, and bodies of animals, the stars and planets and their movements, the winds and the clouds, and so on through the list of physical things and their movements. On the other hand are the thoughts and feelings of men and of other animals: ideas, opinions, memories, hopes, fears, pleasures, pains, smells, tastes, and so on through the list of states of mind. Psychology, the science of mental facts or of mind, deals with the latter. EXERCISE Which of the following words refer to mental facts? Which refer to physical facts? Which refer sometimes to mental and sometimes to physical facts? Gas, tree, sympathy, money, desire, wish, dog, stone, dreams, headache, inventiveness, inch, pound, taste, intelligence, heavy, sour, oxygen, electricity, fatigue, pleasure, loud, observe, remember, image, teeth. (23: 1-2) Example of students being assisted and required to discover meanings. Finally, a fourth type of procedure is illustrated by the following quotation from the "Outlines of Economics" (see above, p. 171), in which the student's attention is called to certain familiar examples and he is then required to work out the answers to questions in order to discover the meanings for the terms under consideration. II. Means of Satisfying Wants Means of satisfying wants are called goods. Goods, which may be material or nonmaterial, are characterized by the quality of utility the capacity to satisfy wants. The following diagram suggests a descriptive classification of goods: Means of satis Economic goods (have utility, Material (wealth) Nonmaterial (services) The economist does not concern himself with these QUESTIONS 1. Does every good possess utility? Is everything which possesses utility a good? 2. Have the following utility: whisky, a gambler's pack of cards, clothes of an obsolete fashion, opium, grand opera, air? 3. Which has the greater utility, a diamond or a barrel of flour? the rare first edition of an old book or a modern copy, better printed and better bound? Why? 4. Are the following appropriable: (a) a loaf of bread; (b) a coal mine; (c) sunshine; (d) the Mississippi River; (e) a public park; (f) a band concert? What is meant by appropriable? 5. Give examples of nonmaterial economic goods, of nonmaterial free goods, and of material free goods. 6. Should the economist be as much concerned with nonmaterial as with material economic goods? Can we say that one class is more important than the other? 7. Make a list of things which are clearly wealth. 8. Make a list of things which are clearly not wealth. 9. Make a list of things concerning which you are in doubt as to whether they are wealth. 10. Define wealth. 11. Are the following wealth: an ocean steamship; a pleasure yacht; a ship on the bottom of the ocean; gold in the mine; gold to a shipwrecked sailor on a desert island; a wooden leg; health; eyesight; a waterfall; a head full of useful knowledge; water? 12. "A thing may be wealth though it is not useful—for example, an Indian arrowhead." Comment. 13. Is an encyclopedia wealth? among Indians? 14. Could a thing that was wealth at one time cease to be wealth at some other time? Could the reverse be true? Why? 15. If a coat should go out of style, would it still be wealth? 16. What distinguishes wealth from services? 17. Should we consider services which have a tangible result more important than those which do not? Give several illustrations of each kind. 18. From the point of view of the economist, could you accept as a definition of wealth (a) means of satisfying wants; (b) things which make for welfare; (c) material means of satisfying wants; (a) material things upon which labor has been expended? 19. Are the following wealth: a courthouse; a warship; a city hall; a public library? 20. How do you distinguish between social wealth and private wealth? Does social wealth include more than private wealth? 21. When a United States gold certificate is destroyed, is wealth destroyed? 22. Is a railroad bond wealth? Is a patented invention? a fireinsurance policy? 23. Suppose a new source of mechanical power should become available at one fourth the cost of steam power. What would be the effect on wealth in general? Would any individuals be made less wealthy by the new discovery? 24. If wealth increases, will there be greater well-being? What is the relation of wealth to well-being? 25. "To be wealth a thing must be scarce." Is that equivalent to saying that the less we have of things, the better off we are? What do you mean by scarce? 26. Is a man's wealth measured by the number or bulk or weight of his possessions or by their money value? Is a scarce article likely to command a higher price than one that is common? Does this imply that wealth is increased by scarcity of goods? 27. Should you accept as true the statement that the scarcity of certain desirable articles, such as jewels, may enhance the comparative wealth of an individual, but that general welfare is promoted by abundance of the commodities which people desire? Why? (17: 4-6) ་་ An excellent opportunity for comparing three lessons of different types on the same topic is afforded in Thorndike's Principles of Teaching" (pp. 167-170). The topic is Tense in grammar. (1) The first lesson merely gives the definitions, with few examples, and at the end provides a list of questions. The answers to these are the statements in the paragraph that has preceded them, in exactly the same order. Such a lesson merely provides for the verbatim learning of general statements that are not understood. (2) The second lesson gives examples first, then the names of the various tenses and some abstract discussion of inaccuracies in using some of the technical terms, such as present tense. (3) The third lesson begins with familiar examples and sets questions which require the student to discover the various ways in which verbs may be used to indicate differences in time. It then gives the technical terms to designate the different tenses and provides practice in picking out and using verbs in different tenses. General questions concerning best method to use. All of these examples of methods which we find used in the textbooks to teach abstract and general meanings and propositions suggest the following questions for consideration in connection with this type of learning: I. What is the value of familiar examples or illustrations? 2. What is the value of analytical discussion by the teacher versus analytical study and discovery by the pupils ? 3. What is the value of a definition? Is it necessary? Should it come before or after the meaning has been acquired? Should it be phrased in technical language or in ordinary language? In order to secure some light on these questions, we shall discuss the nature of the process of learning abstract and general meanings. Untutored method of learning may contain suggestions. A brief discussion of the way in which general meanings or abstractions are acquired in ordinary life may throw some light on the best procedure to be followed in teaching. I say may because the best or most economical and effective process of learning under instruction might differ very greatly from the natural, untutored process. Abstracting is a process of selecting a single aspect for separate attention. For our purposes the process of abstraction or abstracting may be thought of as getting acquainted with some aspect of a situation apart from its other |