Lives of Eminent Philosophers 7.74 — Diogenes Laërtius on the Stoics

Diogenes Laërtius, Lives of Eminent Philosophers 7.74

Reported speech · Diogenes Laërtius on the Stoics

An inferential proposition is true if starting from a true premiss it also has a consequent conclusion, as e.g. “Since it is day, the sun is above the horizon.” But it is false if it starts from a false premiss or has an inconsequent conclusion, as e.g. “Since it is night, Dion is walking,” if this be said in day-time. A causal proposition is true if its conclusion really follows from a premiss itself true, though the premiss does not follow conversely from the conclusion, as e.g. “Because it is day, it is light,” where from the “it is day” the “it is light” duly follows, though from the statement “it is light” it would not follow that “it is day.” But a causal proposition is false if it either starts from a false premiss or has an inconsequent conclusion or has a premiss that does not correspond with the conclusion, as e.g. “Because it is night, Dion is walking.”