12. ILLUSTRATIVE EXERCISES.
1a. The italicized words in the following propositions are predicables because they are affirmed of the subject:
(1) “This man weighs one hundred fifty pounds.”
(2) “A bird is a feathered biped.”
(3) “The earnest teacher is an indefatigable worker.”
(4) “Walking is the most beneficial outdoor exercise.”
1b. Underscore the predicables in the following:
(1) “All men are rational.”
(2) “Teachers must be just.”
(3) “Every form of unhappiness springs from a wrong condition of the mind.”
(4) “Calmness of mind is one of the beautiful jewels of wisdom.”
2a. To clarify our ideas it is an excellent plan to select a group of words belonging to the same genus with a view of defining them as simply and expeditiously as possible. As an illustration building may be selected as a genus. The word kind will suggest to us the species, such as dwelling, church, theatre, school, barn, bird-house, granary and smoke-house. Next it is necessary to discover the basis of distinction. This seems to be the use to which the building is put. Now we are ready for the definitions:
| Species | Genus | Differentia | |
| A | dwelling | is a building | where people live. |
| A | church | is a building | where people worship. |
| A | theatre | is a building | where people act. |
| A | school | is a building | where children are taught. |
| A | barn | is a building | where domestic animals, hay and grain are kept. |
| A | bird-house | is a building | designed for birds. |
| A | granary | is a building | where grain is stored. |
| A | smoke-house | is a building | where meat is smoked. |
2b. By selecting man as the genus, define the terms Caucasian, Mongolian, Ethiopian, Malay and American Indian. Treat the term chair in the same manner.
3a. One may easily distinguish a property from an accident by asking himself the question, “Would subtracting the attribute from the term alter its identity”? For example in the following, I find that the words italicized are properties because subtracting each from the term changes its identity:
| Term | Attributes |
| man | age, rationality, possessions. |
| book | binding, leaves, size, color, contents. |
| radium | emits intense light and heat, costs a million dollars a pound. |
| snail | air-breathing mollusk, moves slowly. |
| slush | soft mud and snow, six inches deep. |
3b. Indicate the common attributes of the following terms, underscoring the properties: Tree, teacher, garden, house, river.
4. The rules summarize well the essentials of the subject matter of the logical definition. Therefore, it is highly important for the student to have these rules at the “tip of the tongue.” With this in view a device of this nature may be helpful. Make each letter of the word rules stand for the initial letter of a suggestive word in each of the five rules. For example: r (repeat), u (unambiguous), l (language affirmative), e (essential), s (same size).
With a little study “r and repeat,” “u and unambiguous,” “l and language affirmative,” “e and essential,” “s and same size” may be firmly linked together in the memory. Repeat suggests the third rule, do not repeat the name, etc.; unambiguous, the fourth rule,not ambiguous language, etc.; language affirmative, the fifth rule; essentials, the first rule; same size, the second rule, subject and predicate must be of same size. The fact that the rules are not recalled in order of treatment is inconsequential.
It is the writer’s experience that fifteen minutes of concentrated study upon this device or one similar to it will indelibly stamp upon the mind these troublesome rules.
The student may be able to devise a more helpful keyword.