(7) Five rules summarize the requirements to which a logical definition must conform. In a word or two these five rules are: Every logical definition must (1) state the genus and differentia, (2) be equivalent to the species defined, (3) not repeat the name to be defined, (4) not be expressed in obscure language, (5) commonly be affirmative. (8) Some terms are too high (summum genus), some too low (infima species), some too peculiar (sui generis) to come within the province of logical definition. =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.