Some contracts must be in writing, including the sale of real estate or a lease of more than 12 months. Not all agreements between the parties are contracts. It must be clear that the parties intended to enter into a legally binding contract. Although an oral contract is always legal (except in certain situations), most contracts are documented in writing. Contracts have become more and more detailed nowadays, and every effort is made to clarify all possibilities and contingencies. If the contract contains uncertain or incomplete clauses and all options for resolving its true meaning have failed, it may be possible to separate and invalidate only the relevant clauses if the contract contains a severability clause. The severability test of a clause is an objective test – whether a reasonable person would consider the contract to exist even without the clauses. As a general rule, inseparable contracts require only the essential performance of a promise and not the full or complete execution of a promise of payment security. However, a non-separable contract may contain express clauses that expressly require the full performance of an obligation.  Defeat these countries to determine whether an alleged contract is (1) void or (2) voidable. Null treaties may not be ratified by either party.
Questionable treaties can be ratified. Contract law is based on the principle expressed in the Latin expression pacta sunt servanda (“Agreements must be respected”).  The common law of contracts arose from the assumpsit order, which was originally a trust-based offence.  Contract law, as well as tort, unjust enrichment and restitution, fall under the general law of obligations.  Courts generally do not eject “reasonableness” from consideration if consideration is found to be “sufficient”, sufficiency being defined as meeting the legal test, while “reasonableness” is subjective fairness or equivalence. For example, agreeing to sell a car for a penny may constitute a binding contract (although the transaction, if it is an attempt to avoid taxes, will be treated by the tax authorities as if a market price had been paid).  The parties may do so for tax purposes in order to disguise donation transactions as contracts. This is called the pepper rule, but in some jurisdictions, the penny may represent a legally inadequate nominal counterpart. An exception to the adequacy rule is money, where a debt for “agreement and satisfaction” must always be paid in full.
    Many contracts contain a choice of jurisdiction clause specifying where disputes relating to the contract are to be heard. The clause may be general and may require that any matter arising out of the contract be filed in a particular state or country, or it may be necessary for a case to be filed in a particular court. For example, a jurisdiction clause may require that a case be filed in the State of California, or more specifically, may require that the case be filed in Los Angeles County Superior Court. However, in a less technical sense, a condition is a generic term and a guarantee is a promise.  Not all contractual terms are referred to as contractual clauses. Representations, which are often pre-contractual, tend to be less strictly enforced than conditions, and material misrepresentations have always been a reason for prosecution for illegal deception. Safeguards were applied regardless of materiality; In modern U.S. law, the distinction is less clear, but safeguards can be applied more strictly.
 Expressions of opinion can be considered a “mere trait.” In the United States, an unusual type of unenforceable contract is a personal employment contract to work as a spy or secret agent. .