Some S is P is called the Particular Affirmative, symbol I (the second vowel of affIrmo).
Some S is not P is called the Particular Negative, symbol O (the second vowel of negO).
The distinction between Universal and Particular is called a distinction in Quantity; between Affirmative and Negative, a distinction in Quality. A and E, I and O, are of the same quantity, but of different quality: A and I, E and O, same in quality, different in quantity.
In this symbolism, no provision is made for expressing degrees of particular quantity. Some stands for any number short of all: it may be one, few, most, or all but one. The debates in which Aristotle's pupils were interested turned mainly on the proof or disproof of general propositions; if only a proposition could be shown to be not universal, it did not matter how far or how little short it came. In the Logic of Probability, the degree becomes of importance.
Distinguish, in this Analysis, to avoid subsequent confusion, between the Subject and the Subject Term, the Predicate and the Predicate Term. The Subject is the Subject Term quantified: in A and E,[1] "All S"; in I and O, "Some S". The Predicate is the Predicate Term with the Copula, positive or negative: in A and I, "is P"; in E and O, "is not P".
It is important also, in the interest of exactness, to note that S and P, with one exception, represent general names. They are symbols for classes. P is so always: S also except when the Subject is an individual object. In the machinery of the Syllogism, predications about a Singular term are treated as Universal Affirmatives. "Socrates is a wise man" is of the form All S is P.
S and P being general names, the signification of the symbol "is" is not the same as the "is" of common speech, whether the substantive verb or the verb of incomplete predication. In the syllogistic form, "is" means is contained in, "is not," is not contained in.
The relations between the terms in the four forms are represented by simple diagrams known as Euler's circles.
Diagram 5 is a purely artificial form, having no representative in common speech. In the affirmations of common speech, P is always a term of greater extent than S.