the.com/subcontrary
Two claims that can both be true, but never both false at once.
means In logic, describing a pair of propositions—classically the particular affirmative ('Some S are P') and particular negative ('Some S are not P')—that cannot both be false together, though they may both be true.
from From Latin sub- ('under') and contrarius ('opposite, set against'), itself from contra ('against'). The 'contrary' family runs deep through logic, where 'contraries' are claims that can't both be true; 'subcontraries' sit beneath them on the medieval Square of Opposition—the diagram logicians drew to map how propositions clash and agree—holding the mirror-image relation: they can't both be false. The 'sub-' literally marks their lower place on that square.
- logic origin
- From Aristotle's square of opposition diagram
- the rule
- At least one must be true, always
- example pair
- Some cats fly; some cats do not
- geometry too
- Names a circle inside another touching internally
- opposite kin
- Contraries can both be false, never both true
aristotelian logic square — two propositions that cannot both be false simultaneously in the traditional square of opposition (e.g., 'some s are p' and 'some s are not p')