Definitions

from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. The process of obverting or the condition so resulting.
  • n. Logic Inference of the obverse of a proposition.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. The act of turning toward or downward.
  • n. An immediate inference that denies the opposite of something previously affirmed.

from the GNU version of the Collaborative International Dictionary of English

  • n. The act of turning toward or downward.
  • n. The act of immediate inference, by which we deny the opposite of anything which has been affirmed. This is also described as “immediate inference by privative conception.”

from The Century Dictionary and Cyclopedia

  • n. The act of obverting or turning toward some person or thing, or toward a position regarded as the front.
  • n. In logic, same as conversion, or the transposition of the subject and predicate of a proposition.
  • n. In logic:
  • n. The taking of the contranominal of the inverse.

Etymologies

Latin obversio a turning towards. (Wiktionary)

Examples

  • It turns out that Strawson's revision of truth conditions does preserve the principles of SQUARE (these can easily be checked by cases), [27] but not the additional conversion principles of [SQUARE], and also not the traditional principles of contraposition or obversion.

    The Traditional Square of Opposition

  • These are the theory of the syllogism and the doctrines of contraposition and obversion.

    The Traditional Square of Opposition

  • A similar thing happened with the principle of obversion.

    The Traditional Square of Opposition

  • Excluded Middle, 'not-wise' is to be affirmed; and _Some men are not-wise_, is by obversion equivalent to _Some men are not wise_.

    Logic Deductive and Inductive

  • If it be true that _All men are wise_, it is false that _Some men are not wise_ (equivalent by obversion to _Some men are not-wise_); or else, since the 'Some men' are included in the

    Logic Deductive and Inductive

  • Take any universal affirmative proposition; convert it by obversion

    Logic Deductive and Inductive

  • Still, given any proposition in the form _A is either B or C_, we can state the propositions that give the sense of obversion, conversion, etc., thus:

    Logic Deductive and Inductive

  • Similarly, _No men are wise_, being by obversion equivalent to _All men are not-wise_, is incompatible with _Some men are wise_, by the same principle of Contradiction.

    Logic Deductive and Inductive

  • Hence, since _The sky is blue_ becomes by obversion, _The sky is not not-blue_, we may also infer _The sky is not red_, etc.

    Logic Deductive and Inductive

  • Similarly, if it be false that _No men are wise_, which by obversion is equivalent to _All men are not-wise_, then it is true at least that

    Logic Deductive and Inductive

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