Contracts That Enforce Themselves With Code
A smart contract is code on a blockchain that automatically executes when its conditions are met, moving money or assets without anyone enforcing it. It removes the need for trust and the ability to fix mistakes.
Code That Executes Itself
A smart contract is code stored on a blockchain that automatically executes when its conditions are met, moving money or assets according to its rules without anyone needing to enforce it. Where a traditional contract requires parties, and ultimately courts, to enforce its terms, a smart contract enforces itself: when the conditions in the code are satisfied, the code runs and does what it says, automatically and irreversibly.
This automatic self execution is the core innovation, removing the need for a trusted party to enforce the agreement, since the code does it. It enables the automated, intermediary free finance of decentralized finance and many other blockchain applications, since agreements can be encoded and executed by code rather than enforced by institutions. But it also removes human judgment and the ability to fix mistakes, since the code runs as written regardless of intent or error, which is both the power and the danger of smart contracts.
A normal contract needs someone to enforce it. A smart contract enforces itself, running its code automatically. That removes the middleman and also removes the judge who could fix a mistake, since the code does exactly what it says, error or not.
How They Work
A smart contract encodes an agreement as rules in code, and when the specified conditions are met, the code automatically executes the agreed actions, moving money or assets as programmed.
| Feature | Effect |
|---|---|
| Conditions in code | The rules of the agreement |
| Automatic execution | Runs when conditions are met |
| No enforcer needed | The code enforces itself |
| Irreversible | Runs as written, cannot be undone |
The automatic execution means that once deployed, the contract runs without anyone needing to trigger or enforce it, doing exactly what the code specifies when the conditions occur. This removes the need to trust a party to fulfill the agreement, since the code fulfills it automatically, and it removes the need for enforcement, since the code cannot fail to execute. But it also means the code runs exactly as written, with no room for judgment, interpretation, or correction, so if the code has an error or does not match the intent, it still executes as written, which is the source of both the reliability and the risk.
What They Enable
Smart contracts enable the automated, intermediary free applications of blockchains, since agreements can be encoded and executed by code rather than requiring institutions to enforce them. Decentralized finance relies on smart contracts to run lending, trading, and other services automatically, without banks or brokers, since the code handles the functions that institutions would otherwise perform.
Beyond finance, smart contracts can automate any agreement whose conditions can be encoded, from insurance that pays out automatically when conditions are met, to supply chain agreements, to any arrangement that can be reduced to code and executed automatically. The vision is to replace agreements that require trust and enforcement with code that executes automatically, removing intermediaries and the need for trust across many domains. This is the transformative promise of smart contracts, enabling automated, self executing agreements that do not need institutions to enforce them, which underlies much of the ambition of blockchain technology beyond simple currency.
The Danger of No Undo
The irreversibility and automatic execution that make smart contracts powerful also make them dangerous, since the code runs as written with no ability to fix mistakes or reverse errors. If a smart contract has a bug, or does something unintended, it still executes, and the results cannot be undone, which has caused enormous losses when flawed contracts moved or destroyed funds irreversibly.
The phrase that code is law captures this: the code does exactly what it says, and there is no judge, no appeal, no correction, so a mistake in the code is executed and permanent. This has led to major losses from bugs and exploits, where flawed smart contracts were manipulated or malfunctioned, moving funds irreversibly, with no way to recover them since the code executed as written. The lack of human judgment and the inability to undo mean that the correctness of the code is everything, and any flaw is catastrophic and permanent, which is the fundamental danger of smart contracts and why their security and correctness are so critical, since the automatic, irreversible execution that removes the need for trust also removes the safety net of human intervention and correction.
The Bottom Line
A smart contract is code on a blockchain that automatically executes when its conditions are met, enforcing an agreement without a trusted party, which removes the need for intermediaries and enables the automated, intermediary free applications of blockchains, from decentralized finance to any agreement that can be encoded. But the automatic, irreversible execution that removes the need for trust also removes human judgment and the ability to fix mistakes, since the code runs exactly as written regardless of error or intent, and cannot be undone. This makes the correctness of the code everything, since any flaw is executed and permanent, which has caused enormous losses and is the fundamental danger of smart contracts, the flip side of the power of contracts that enforce themselves with code.