The statements of ordinary conversation are usually not expressed in terms of the four elements, but must be, before they can be used in testing arguments.
(4) One word usually constitutes the grammatical subject while a word with all its modifiers goes to make up the logical subject. The verb with any predicate word is the grammatical predicate. The logical predicate is all which follows the copula—it may include the predicate-word and all its modifiers as well as the modified object.
(5) Categorical propositions are divided into four kinds; universal affirmative (A), universal negative (E), particular affirmative (I), particular negative (O). For the sake of brevity these four are respectively denoted by the vowels A, E, I, O.
An A proposition is one in which the predicate affirms something of all of the logical subject.
An E proposition is one in which the predicate denies something of all of the logical subject.
An I proposition is one in which the predicate affirms something of a part of the logical subject.
An O proposition is one in which the predicate denies something of a part of the logical subject.
Every proposition must be reduced to one of the four types before it can be used as a basis of argumentation.
It is incumbent on the student to recognize these four types with precision and accuracy.
(6) There are a few proposition types which are recognized as being illogical in form. These may be defined as follows: