"S" and "P" here are not sentence letters. Rather, they stand for classes of things. For example, in "All apples are tasty", "S" would stand for "apples." We use "S" to indicate the grammatical subject position in a categorical proposition and "P" to indicate the predicate position. Each categorical type can be charactered in terms of its quantity and its quality:

Quantity: Each categorical sentence is either universal or particular. The universal categorical sentences are:

The particular categorical sentences are:

Quality: Each categorical sentence is either affirmative or negative. The affirmative ones are:

The negative ones are:

Each type of categorical sentence gets a letter name, and these are boxed letters next to their corresponding categorical forms above. The origin of these letter names is not arbitrary. They come from the Latin words:

AffIrmo
nEgO

The A and I categorical sentences are affirmative (affirmo) and the E and O categorical sentences are negative (nego).

Since each categorical sentence has just one quantity and just one quality, we can completely characterize any categorical sentence by giving its quantity and quality:

The following exercise will give you practice in recognizing the four types of categorical propositions.

table of contents		List of Exercises