Full Idea
There are four 'perfect syllogisms': Barbara (every M is P, every S is M, so every S is P); Celarent (no M is P, every S is M, so no S is P); Darii (every M is P, some S is M, so some S is P); Ferio (no M is P, some S is M, so some S is not P).
Gist of Idea
The four 'perfect syllogisms' are called Barbara, Celarent, Darii and Ferio
Source
Engelbretsen,G/Sayward,C (Philosophical Logic: Intro to Advanced Topics [2011], 8)
Book Reference
Engelbretsen,G/Sayward,C: 'Philosophical Logic: Intro to Advanced Topics' [Continuum 2011], p.142
A Reaction
The four names are mnemonics from medieval universities.