Bocardo

A form of syllogism in scholastic logic. The name is from a medieval mnemonic poem, where its vowels reflect the syllogism's standard form of OAO-3. 

Some M are not P.	O - particular negative
All M are S.	A - universal affirmative
Therefore, some S are not P.	O - particular negative

Bocardo shares its name with a prison in Oxford, England. Some have suggested the prison's name playfully references Bocardo being a particularly awkward form to 'get out of', in that it cannot be directly reduced to the first figure and must instead be proven indirectly by special means. 

Barbara, Celarent, Darii, Ferio que prioris;
Cesare, Camestres, Festino, Baroko secundae;
Tertia, Darapti, Disamis, Datisi, Felapton,
Bokardo, Ferison, habet; Quarta in super addit
Bramantip, Camenes, Dimaris, Fesapo, Fresison

Bo*car"do (?), n. [A mnemonic word.]

1. Logic

A form of syllogism of which the first and third propositions are particular negatives, and the middle term a universal affirmative.

Baroko and Bocardo have been stumbling blocks to the logicians. Bowen.

2.

A prison; -- originally the name of the old north gate in Oxford, which was used as a prison.

Latimer.

© Webster 1913.