This means that a logical definition should contain the species, the proximate genus and the differentia. As the terms species, genus and differentia have been explained, it will be sufficient to briefly illustrate this rule.
Logical According to the First Rule.
(1) A species
bird is a genus
biped with differentia
feathers.
(2) A species
mascot is a genus
person differentia
supposed to bring good luck.
(3) species
Religion is a genus
system of differentia
faith and worship.
(4) A species
moonbeam is a genus
ray of light differentia
from the moon.
Illogical According to the First Rule.
(1) A man is a rational animal.
(“Biped” is the proximate genus, not “animal.”)
(2) A Connotative term always denotes both an object and an attribute.