In the English case Barry v Davies, it was found that an auctioneer and a buyer had entered into a secondary contract.  It has been found that, although the main contract does not concern the incense, the benefits granted to the bid represent a good consideration for the increase in the price of the offer.  Consider De Lassalle v. Guildford, a loan contract case in which the latter rented a house at the first. The landlord promised to repair the runoff before the tenant moved in. This promise was considered by the court to be a secondary contract that allowed the tenant to sue if he found that the exits had not been fixed as promised. Sometimes a term is ambiguous and needs to be clarified from the outside. What is “wood,” for example? When developing a treaty, the parties sometimes forget to define such a key concept. In type v. Smith, the parties have denied the importance of this clause in an agreement.  The Mississippi Supreme Court allowed the plaintiff to introduce parol evidence to show the importance that the parties themselves placed on the words of their own written contract. The court allowed the plaintiff to introduce evidence of a prior written agreement of the parties in the definition of wood, which was “commercial pine wood,” to explain the meaning of the word in the current contract. This rule prevents parties from changing the importance of written contracts with oral or tacit agreements that are not included in the original contract, the latter impairing their integrity.
This means that, when a contract is available in writing, subsequent agreements that are not entered into in writing are not proven in a contractual dispute. There are, however, several exceptions to this rule. A support contract is a contract by which the contracting parties enter into or promise another contract. The two treaties are therefore linked and can be applied, even if they are not a constructive part of the original treaty.  In JJ Savage and Sons Pty Ltd v. Blakney, a mere expression of opinion was not deemed sufficient to be kept as a promise. In Crown Melbourne Limited v Cosmopolitan Hotel (Vic) Pty Ltd, a statement from a landlord to the tenants considered when negotiating a lease agreement that they are “supported during the extension” would not bind the lessor to offer another five-year lease.  A security contract, if forged between the same parties as the main contract, must not be contrary to the main contract. In other words, if the term was agreed before the formal contract was concluded (but was still in place and could not be executed before the end of the second term), the first term will remain eligible.  In essence, security contracts cannot contradict an element of the main contract or the rights that flow from it.  Despite its resemblance to the word “watchword,” the parol rule of evidence has nothing to do with criminal law.