OCHI MARIA CHIKAMSO
Unjust enrichment, the doctrine of modern contract dates back to the 13th century English Law, known as the “Action of Assumpsit” which developed from “Trespass on the Case.” The courts at that time did not recognize our modern concept of breach of contract. According to Ranulf Glanvill, a famous legal scholar, he wrote just before the year 1200 thus, “It is not the custom of the Lord King to protect the private agreements nor does it concern itself with such contracts as can be considered private agreements.”  However, in the early days of English common law, the forms of actions known as Writs provided a proactive approach to the categories of civil liability and according to Maitland’s words “the forms of action we have buried, but they still rule us from their graves.”  This article seeks to proffer an overview of the historical development of our modern contractual terms and law.
FORMS OF ACTION
Two forms of action particularly existed at that time which was contractual, and they were Writ of Covenant and Debt.  These writs commanded the defendants to perform an act e.g. fulfil a promise.
The action of the covenant was only available to enforce an agreement or promise made in writing and under seal usually referred to as a “Deed.” Individuals were unable to employ this document in informal affairs, so the action of the covenant had limited utility for enforcing promise and was thus one of the limitations.  This writ applied rather to a promise to pay money.
The second writ, which was Writ of Debt, was two-fold. They were the Writ of Debt on The Obligation (debt sur obligation) and Writ of Debt on The Contract (debt sur contract). In actions, which concerned obligating someone to pay, the Writ of Obligation came in handy. If a defendant admitted a debt in sealed writing (formal promise), an obligation would arise not because the defendant promised to pay as it is in a writ of the covenant but rather the obligation arose because he admitted he owed and that was the difference between a deed on the obligation and writ of covenant. It also worked under a written and sealed agreement. Thus, instead of saying a defendant promised to pay money, a plaintiff would claim that he owed it.
Writ of Debt on Contract also known as debt sur contract covered an informal agreement. It covered admittance of a debt owed as far as it was not in a sealed writing. Thus, it covered oral admittance or admittance in writing so far it was not under a seal and a deed was not necessary. This was the reason it covered informal agreements. Informal agreement came in the form of loans, purchase of goods, quid pro quo (agreement to pay for services received) etc. It is very important to note that while the Writ of Covenant covered promises made, although it must be in writing and under a seal, Writ of Debt both sur obligation and sur contract covered admittance of a debt owed and not a promise made.
Despite this benefit, the debt sur contract has its limitations. Primarily, it was not available unless the plaintiff claimed that the defendant owed him a specific sum of money and not for monetary damages, thus it was useless for enforcing monetary damages for breach of promise to pay a debt owed to the plaintiff in a situation where the agreement fails. This limitation did not affect the usage of the action of debt sur contract to enforce informal promises, insofar as the plaintiff could claim a specific sum or prove that the defendant had received a quid pro quo for the accrued debt he owed.
Another limitation was that it provided no useful remedy for the improper performance (misfeasance) of an informal agreement. Suppose a countess took a pair of shoes to a cobbler for repair and the cobbler performed the work badly thus damaging the shoes further. The countess could not seek a remedy in covenant because it was a routine transaction, and one would not expect a sealed document nor will the action of debt sur contract apply, because the damage caused by the improper performance was not a specific sum.
Another limitation of debt sur contract was that the court rules permitted the defendant accused of owing a debt to have the benefit of “wager of law.” This benefit allows the defendant to appear in court with oath helpers each of whom would swear that the defendant was a credible person and was not indebted to the plaintiff. The defendant will succeed, if done successfully. 
Due to these various hardships and limitations, especially inability to recover for damages due to breach of an agreement, litigants turned to the law of tort in particular, the Writ of Trespass which led to the emergence of the doctrine of assumpsit. It was different from debt or covenant in the sense that while debt demanded the specific recovery of a debt, covenant demanded the actual performance of a promise made. However, the Writ of Trespass came into action in such a way that a wrongdoer was compelled to compensate in monetary value for damages because of the defendant’s wrongdoing.
EMERGENCE OF THE WRIT OF TRESPASS AND WRIT OF TRESPASS ON THE CASE
This form of action known as a Writ of Trespass generally applied to public wrongs, such as breach of the King’s peace. It is the unlawful interference using direct force with another person or his property or rights. However, the courts later recognized that a writ of trespass could lie even without an allegation that the defendant had acted with force and arms against the King’s peace in the Humber Ferryman’s Case.  The court recognized a new form of action known as a Writ of Trespass on the case also known as action on the case or simply cases, which allowed one to recover for injury/damage that resulted indirectly or by the negligence of the defendant’s actions. It extended to private wrongs.
In Bukton v Townsend,  traditionally known as The Humber ferryman’s case, the defendant overloaded a boat with the plaintiff’s horses, which he sought to ferry across the Humber River. The plaintiff’s horse, which was among the horses, fell overboard and died. Plaintiff sued in tort for trespass. There was no sealed document, and in the previous law, the requirement was to sue for breach of a covenant. The defendant argued that the action be brought under the Writ of Covenant. The King’s Bench held that the plaintiff was right in bringing the action under tort. The claim was against the killing of the horse (liability for the negligent breach of a contractual undertaking) and not merely the failure to transport it and thus it was not vital to bring a documentary proof of covenant.
In Waldon v Marshall,  the plaintiff alleged that the defendant, a horse doctor, had undertaken to cure his horse but owing to the negligent performance, the horse died. The defendant argued that it be brought under trespass generally, but the court held that the action was properly laid on trespass on the case. Thus, where there was a breach of an express undertaking by a negligent act or wrong (misfeasance), the offended party could use an action on the case.
By the 15th century, it was trite law that the offended party could use an action on the case to recover damages for improper performance of a voluntary agreement. It did not apply to nonfeasance i.e. failure to render any performance at all. For nonfeasance, one had to invoke the action of the writ of the covenant where he could recover, if only he had the specialty of a sealed document. Nevertheless, by the 16th century, exceptions to this rule came and the plaintiff could recover for nonfeasance and misfeasance with or without a sealed document. This completely superseded the Writ of Covenant. What the plaintiff needed was a “special assumpsit” to prove deceit on the part of the defendant for breach of an express agreement that is a failure to carry out an express agreement.
In Somerton’s case,  Somerton had retained Colles as Counsel in the purchase of a manor. Colles fraudulently and falsely procured the manor for another. Court held that a mere failure to perform the undertaking would not give Somerton an action on the case; the appropriate form of action would have been covenant and this would require a seal. It was however different where the counsel betrays his client and becomes counsel for another. For here, deceit would lie. Similarly, in Shepton v Dogge,  also known as Doige’s case, in which the defendant undertook to enfeoff the plaintiff within fourteen days but instead, enfeoffed a third party. The defendant claimed against the plaintiff’s bill of deceit on the ground that the action should have been in the covenant, but again the verdict went in favour of the plaintiff. The defendant’s act of enfeoffing the third party had rendered him liable in deceit.
By the 16th century, lawyers recognized a distinct specie of action on the case, known as Assumpsit. It became the typical phrase in pleadings. Assumpsit took over for such issues such as the claim that the defendant failed to fulfill an agreement leading to a breach of the agreement.
DEFINITION OF ASSUMPSIT AND OTHER FORMS OF ASSUMPSIT
Assumpsit  is a form of action, for the recovery of damages for the non-performance of, a parol or simple contract; or, in other words, a contract not under seal, nor of record.
A new form of assumpsit also emerged known as ‘Indebitatus assumpsit.’ It became possible to sue in assumpsit if the defendant owed a debt and then violated a fresh promise to pay it. It simply meant, “Being indebted, he promised.” This development allowed such a range of lawsuits based on promises to private parties and thus, claimed the name “general assumpsit.” The issue of using assumpsit even when an action of debt could be available came up. This was because of the more desirable course of the assumpsit where the defendant would not be able to use the benefit of wager of law as he would in debt sur contract.
Two issues arose as to whether assumpsit could be used as a form of action in lieu of debt.  The first issue was that of proving the subsequent promise to pay as regards the Indebitatus Assumpsit, while the second issue was as regards to the practice of the King’s Bench and the Court of Common Pleas.
In the King’s Bench, the plaintiff did not need to prove the subsequent promise. The Court of Common Pleas however disagreed. However, the case of Slade V Morley  established that assumpsit could be used in lieu of debt at the plaintiff’s election and that the law would imply a promise to pay the debt, from the existence of the debt itself.  It was not possible though to bring an action in assumpsit where the proper action was debt sur obligation. The reason for this was that assumpsit applied only to agreements made orally or in writing but not under seal.
Assumpsit became like a saviour coming to the rescue of parties to contract cases. William Blackstone in his “Commentaries on the Laws of England” he explained that this was the reason The Statute of Frauds was later passed in 1677. 
In the 17th century, actions developed for the recovery of money (had and received), for goods sold i.e. for reimbursement of goods supplied (quantum Valebat) and work/services rendered (quantum meruit).
Claim in action for assumpsit could be in two ways thus:
Common or Indebitatus Assumpsit (implied promise once a debt exists)
Special or express assumpsit (express agreement/promise) 
Where a plaintiff brings an action in lieu of debt sur contract, the plaintiff had to specify how the debt had arisen using the common ways of pleading how the debt arose. It was not sufficient enough for the plaintiff to only allege that the defendant owed a debt, the plaintiff must also show that the defendant promised to pay.
Common ways of pleading how the debt arose are:
For money had and received to the defendant’s use.
Reimbursement for goods sold (quantum Valebat)
For services rendered (quantum meruit)
For money lent
For money due on account stated.
In our recent contractual laws such as unjust enrichment, consideration, there exists the traces of the past common law. For instance, back then, if Oge mistakenly pays money to Nneka, Oge would bring an action for money had and received to the defendant’s use. The law would imply a promise of Nneka to pay the debt. In our modern contractual laws, this is what we refer to as unjust enrichment. In addition, consideration is only necessary for simple/informal contracts and where a claimant brings an action for the breach of contract under a seal, he needs not to prove consideration for the promise. Looking back, the same applied where there was a deed/seal as the action came under the writ of covenant and debt sur obligation, but where it was not under a seal the action came under debt sur contract or assumpsit.
In our current contract laws of unjust enrichment, the doctrine of quantum meruit and actions for money had and received (quasi-contract) are still in use. In addition, the concept of detriment in the present doctrine of consideration is similar to the harm suffered by the plaintiff in the early trespass action, while the benefit to the promisor is similar to the services (quid pro quo) received by the defendant in a debt action.
The abolishment of the doctrine of Assumpsit came was preceded by the Judicature Act 1925. It is clear that the doctrine of assumpsit established what we now refer to as our modern law of contracts.
F. Matiland “The Forms of Action at Common Law: A Course of Lectures” (1963) https://www.worldcat.org/title/forms-of-action-at-common-law-a-course-of-lectures-by-fw-maitland/oclc/5937642 accessed on 28th November 2020
Sir John Baker “An Introduction to English Legal History” (4th Edition, 2004)
Waltham Carrier Case (1321) in London Eyre 1321 86 Seldon Society 286
JW Salmond. “Observations on Trevor and Conversion” (1905) 21 L. Q. R.
(1348) B&M 358
Y. B. Mich. 43 Edw. III, f. 33, pl. 38 (1370)
(1433) B 11 Hen 6 Hil Pl 1. 101
(1442) B Hill 9 Hy VI. 102
Chisholm, Hugh, ed. (1911). “Assumpsit”. Encyclopædia Britannica. 2 (11th Ed.). Cambridge University Press. P. 787.
AWB Simpson ” A History of the Common Law of Contract” at 199
Slade’s case (1598) 4 Co Rep 92b, 76 ER 1074 (1602)
Slade v Morley (1792) Yelv 21, 80 ER 15
Slade v Morley (1688) MooKB 433, 72 ER 677
Maitland, F. W. (1909). “The Forms of Action at Common Law”.
Blackstone, Williams (1771). “Commentaries on the Laws of England.”
Chisholm, Hugh, ed. (1911). “Assumpsit”. Encyclopædia Britannica. 2 (11th Ed.). Cambridge University Press. P. 787.