from
Bouvier's Law Dictionary, Revised 6th Ed (1856)
SPECIAL ASSUMPSIT, practice. Where an action of assumpsit (q.v.) has been
brought on a special contract, and the plaintiff declares upon it, setting
out its particular language, or its legal effect. It is distinguished from a
general assumpsit, where the plaintiff, instead of setting out the
particular language, or effect of the original contract, declares as for a
debt, arising out of the execution of the contract, where that constitutes
the debt. 3 Bouv. Inst. n. 3426.