Conventions, Symbolism, and Relations among Categorical Propositions in Experimental Research
The four forms of categorical propositions (1) through (4) mentioned above are named, and often referred to, respectively, as A, E, I, and O propositions. The (verb) terms of affirmation (e.g., “is,” “are,” and “were”) and negation (e.g., “is not,” “are not,” and “was not”) are referred to as indicating the quality of affirmation