A more thorough explanation:

The leading-object rule, also known as the main-purpose rule, is a doctrine in contract law. It states that if a promise to guarantee someone else's debt is made primarily for the promisor's own benefit, then the promise does not have to be in writing and the statute of frauds does not apply.

For example, if a business owner promises to pay a supplier's debt to ensure that the supplier continues to provide goods to the business, then the leading-object rule applies. The promise is made for the benefit of the business owner, as it ensures a continued supply of goods, rather than for the benefit of the supplier.

The leading-object rule is important because it allows certain promises to be enforceable even if they are not in writing. However, it only applies in specific circumstances where the primary purpose of the promise is for the promisor's own benefit.