As a general rule, an unspoken contract has the same legal force as an explicit contract. However, in the event of a dispute, it may be more difficult to prove the existence and terms of a tacit contract. In some legal systems, contracts for real estate cannot be established on an implicit and effective basis, so the transaction must be made in writing. A tacit agreement is indeed based «on a meeting of spirits which, although not enshrined in an explicit treaty, is inferred as a fact of the behaviour of the parties who, in the light of the circumstances of the mind, show tacit understanding.» Baltimore – Ohio R. Co. v. United States, 261 U.S. 592, 597, 43 S.C. 425, 426-427, 67 L.Ed. 816 (1923).
See also Russell v. United States, 182 U.S. 516, 530, 21 S.C. 899, 904, 45 L.Ed. 1210 (1901) ([T]o giving the Court of Claims Jurisdiction the application must be based on an agreement between the parties – `a meeting of minds`). On the other hand, an agreement implied by law is a «fiction of law» that «implies a promise to fulfill a legal obligation to repay funds obtained as a result of fraud or coercion.» Baltimore – Ohio R. Co., supra, at 597, 43 S.C., at 426. A tacit contract can also be created by the behaviour of the parties so far.
For example, a teenager offers to walk a neighbor`s dog and is rewarded with two movie cards. On three other occasions, the teenager comes to walk the dog and receives two movie cards. But on the last occasion, the neighbor does not produce the cinema cards. The teen has a case of the neighbour having established an unspoken contract by regularly producing movie tickets in exchange for dog walking services. That`s a reasonable assumption. It consists of commitments arising from mutual agreement and the intention to promise if the agreement and promise were not expressed in words. Such contracts are implicit and may result from the conduct of the parties because of facts and circumstances that demonstrate mutual contractual intent. A contract that involves is a real contract. An unspoken contract is a form of tacit contract that is done by non-verbal and not by explicit words. The U.S.
Supreme Court defined it as «an agreement that is effectively implied» as «based on an assembly of spirits that, although not enshrined in an explicit treaty, is derived from the conduct of the parties who, in the light of the circumstances, demonstrate tacit understanding.»  A tacit contract is a legally binding obligation arising from the acts, behaviours or circumstances of one or more parties in an agreement. It has the same legal force as an explicit contract, that is, a contract entered into and agreed upon by two or more parties, voluntarily or in writing. On the other hand, the tacit contract is accepted, but no written or oral confirmation is required. To establish the existence of a tacit contract, it is necessary to show a clear offer, clear acceptance, mutual intention to be bound and reflection. However, these elements can be established by the behaviour of the parties and not by explicit written or oral agreements. While the parties may not have agreed, their behaviour may indicate that there was an agreement. The principles underlying a tacit contract are that no person should receive unfair benefits at the expense of another person and that no written or oral agreement is required to obtain fair play.