7. PROPOSITIONS WHICH ARE NOT NECESSARILY ILLOGICAL.
(1) Analytic and Synthetic Propositions.
An analytic proposition is one in which the predicate gives information already implied in the subject. Thus, “Fire burns,” “Water is wet,” “A triangle has three angles” are analytic propositions because the predicates do not give added information to one who has any conception of the subjects. Because the attribute mentioned by the predicate is an essential one, analytic propositions are sometimes termed essential propositions. Other names for the same kind of proposition are verbal and explicative.
A synthetic proposition is one in which the predicate gives information not necessarily implied in the subject. “Fire protects men from the wild animal.” “A cubic foot of water weighs 621⁄2 lbs.” “The sum of the interior angles of a triangle is equal to two right angles.” These are synthetic because a common conception of the meaning of the subject would not need to include the information given by the predicate. Other names for synthetic propositions are accidental, real and ampliative.
The distinction between analytic and synthetic propositions is not so clear as would on first thought appear. “Fire burns” might give added information to the child or savage who knows only of the light emitted by fire.To them, then, the proposition would be synthetic. The distinction must be based upon the assumption that the same words mean about the same thing to people in general.
This analytic-synthetic division of propositions finds a significance in the domain of philosophy. To the logician the distinction is of slight importance save in the so-called verbal disputes, viz.: disputes which turn on the meaning of words.
(2) Modal and Pure Propositions.
A modal proposition states the mode or manner in which the predicate belongs to the subject. The signs of modal propositions are the adverbs of time, place, degree, manner. Illustrations: “James is walking rapidly.” “Honesty is always the best policy.” “Aristotle was probably the greatest thinker of ancient times.”
A pure proposition simply states that the predicate belongs, or does not belong, to the subject. Illustrations: “James is walking.” “Honesty is the best policy.” “Aristotle was the greatest thinker of ancient times.”
Some logicians refer to modal propositions as being such as indicate degrees of belief. Such words as “probably,” “certainly,” etc., would indicate their modality.
As logic has to do with the pure proposition and not the modal, the difference of opinion is of little import.
(3) Truistic Propositions.
A truistic proposition is one in which the predicate repeats the words and the meaning of the subject. Illustrations: “A man is a man,” “A beast is a beast,” “A traitor is a traitor,” “What I have done I have done.”
The truistic proposition is of little importance except in cases where the subject is used extensionally while the predicate is used intensionally. In the illustration, “A man is a man,” the subject merely stands for a member of the man family, while the predicate may indicate certain manly qualities. Against such ambiguities the logician must be on guard.