The octagon of opposition (1975), p. 353
by Hacker, Edward A.

Copyright according to our policy

Legend

Logic

Aristotelian family

Keynes-Johnson Sigma-4

Boolean complexity

7

Number of labels per vertex (at most)

4

Equivalence between (some) labels of the same vertex

Yes

Analogy between (some) labels of the same vertex

No

Uniqueness of the vertices up to logical equivalence

Yes

Errors in the diagram

No

Geometry

Shape

Octagon (irregular)

Colinearity range

0

Coplanarity range

0

Cospatiality range

0

Representation of contradiction

By central symmetry

Vertex description

Conceptual info

No

Mnemonic support (AEIO, purpurea ...)

Yes

Edge description

Style

Diagram is colored

No

Diagram is embellished

No