To understand why modern contract law focuses heavily on consideration and promises, we must examine the history of English Common Law. Before the 17th century, there was no general "Law of Contract"—instead, there was a rigid Writ System.
1. The Early Writs
In the royal courts of medieval England, a plaintiff could only bring an action if their claim fit into a pre-existing "Writ" issued by the King:
- Writ of Debt: Used to recover a fixed, liquidated sum of money (e.g., A sold B a horse for £10, and B refused to pay). It was limited because it required proof of physical delivery ("quid pro quo") and could be defeated by the archaic practice of "wager of law" (where the defendant brought 11 neighbors to swear they did not owe the money).
- Writ of Covenant: Used to enforce formal promises made under seal (a formal deed). If the promise was verbal or in a simple unsealed letter, the Writ of Covenant was completely unavailable.
2. The Breakthrough: Trespass on the Case and Assumpsit
Because simple verbal agreements had no remedy under the early writs, merchants suffered. To solve this, the courts slowly adapted the tort-like action of Trespass on the Case (wrongful damage caused indirectly).
If a doctor promised to cure a horse but treated it so negligently that the horse died, it was treated as a tortious misfeasance. The legal action was called Assumpsit (Latin for "he undertook"). Over time, the courts expanded Assumpsit from active misfeasance (doing a job badly) to non-feasance (failing to do the job at all).
In Slade's Case, the court established that every executory contract imports an assumpsit (a promise). This meant that the mere existence of mutual promises was enough to sue for breach, effectively killing the rigid old Writ of Debt and birthing the modern, flexible concept of contract law.
3. Will Theory vs. Objective Theory
As contract law developed, two philosophical models competed to explain what makes a contract binding:
- The Will Theory (Subjective): Asserts that a contract is a "meeting of the minds" (consensus ad idem). It focuses on the inner intentions of the parties.
- The Objective Theory: Focuses on external behavior. If a reasonable person would conclude from a party's words or actions that they intended to enter into a contract, they are legally bound, regardless of their hidden, subjective intentions. Modern common law and the Indian Contract Act strongly favor the Objective Theory to protect commercial certainty.