The legal term assumpsit comes from the Latin assumere, meaning “he undertook.” It refers to a promise made to induce someone to engage in some act, or to pay something to another person. Assumpsit may be made orally, or in writing. This is a common-law concept that has to do with whether or not a contract was made, and whether a claim for breach of that contract can be made. To explore this concept, consider the following assumpsit definition.

Definition of Assumpsit


  1. An action for breach of contract
  2. An actionable promise, which may be grounds for a lawsuit


Circa 1600       Latin  assumere   (“he undertook,” or “he has taken upon himself”)

What is Assumpsit

Assumpsit refers to a promise made that induces someone to undertake some action, or to get them to pay money to the party making the promise. It is the basis for a contract, whether the promise was made verbally, or put into writing. An action of assumpsit is a legal action – or civil lawsuit – in which the party who performed the action asks the court to force the promising party to uphold his part of the deal.

There are two types of assumpsit:

  1. Express Assumpsit – A promise is express if the person making the promise (“promisor”) uses clear-cut language to specify what the promise entails.
  2. Implied Assumpsit – A promise is implied if, even without a specific or formal promise, the circumstances, or the party’s actions, suggests the promise exists.

History of Assumpsit

The history of assumpsit is rooted in 14th century common law, where it was used in the royal courts to settle disputes regarding contracts. Prior to the 13th century English law, the king did not get into settling squabbles over private agreements – concerning himself only with royal rights, and disputes between noblemen.

As the kingdom fostered trade, however, the king’s court began hearing actions for breach of contract, assumpsit, and debt. These actions could only be brought if the agreement had been made in writing, and when the contract had been completed, save for a failure to pay the specified sum of money.

It wasn’t until the late 14th century that the courts allowed a plaintiff to sue a defendant who had acted to cure his horse, but whose treatment was so negligent that the horse died. In this example of assumpsit, one party had taken upon himself the responsibility for curing the horse.

Example of Assumpsit Lawsuit

A man was allowed to sue the surgeon who had acted negligently in trying to cure him, maiming him instead. These cases of the time were a sea change in the law’s willingness to permit lawsuits for badly performed duties, or obligations that did not amount to a total failure to perform the terms of the contract. For example, assumpsit here is the undertaking of doing surgery in exchange for payment.

While the surgeon didn’t default on his obligation – he actually did perform the surgery – he did it so poorly that he caused further, permanent damage to the other party.

This type of common law dispute led to modern laws in contract torts and unjust enrichment, beginning in the 19th century. Actual claims of assumpsit became obsolete in the U.S., when the Federal Rules of Civil Procedure (“FRCP”) were adopted in 1938. Most states soon adopted rules of court similar to the FRCP. Some states continue to recognize causes of action for “common counts,” based on assumpsit.

Indebitatus Assumpsit

Indebitatus assumpsit means “to have taken on a debt.” A lawsuit in common law for indebitatus assumpsit was based in a contract, the plaintiff claiming that the defendant had failed to repay, or otherwise satisfy, a debt. Indebitatus assumpsit was most often based on an implied promise.

Related Legal Terms and Issues

  • Breach of Contract – A violation of contract through failure to perform, or through interference with the performance of the contractual obligations.
  • Civil Lawsuit – A lawsuit brought about in court when one person claims to have suffered a loss due to the actions of another person.
  • Common Law – Laws that are based on court or tribunal decisions, which govern future decisions on similar cases.
  • Contract – An agreement between two or more parties in which a promise is made to do or provide something in return for a valuable benefit.
  • Defendant – A party against whom a lawsuit has been filed in civil court, or who has been accused of, or charged with, a crime or offense.
  • Negligence – Failure to exercise a degree of care that would be taken by another reasonable person in the same circumstances.
  • Plaintiff – A person who brings a legal action against another person or entity, such as in a civil lawsuit, or criminal proceedings.