The conditions may be implied because of the actual circumstances or the behaviour of the parties. In the case of BP Refinery (Westernport) Pty Ltd/Shire of Hastings, the Privy British Council proposed a five-step test to determine the situations in which the facts of a case may be subject to conditions. The traditional tests were the “enterprise efficiency test” and the “bystander officious test.” As part of the business test test, first proposed in The Moorcock , the minimum requirements required to give the contract the company`s effectiveness are implicit. In the context of the officious bystander test (named at Southern Foundries (1926) Ltd v Shirlaw , but in fact from Reigate v. Union Manufacturing Co (Ramsbottom) Ltd , a term can only be implied if an “abominable spectator” who is part of the contract negotiations suggests that the parties would immediately agree. The difference between these tests is questionable. An exception arises when advertising makes a unilateral promise, such as offering a reward, as decided in the famous case of Carlill v Carbolic Smoke Ball Co, in 19th century England. The company, a pharmaceutical manufacturer, proposed a smokeball that, if it sniffed “three times a day for two weeks,” would prevent users from catching the “flu.” If the smokeball does not prevent “the flu, the company promised that it would pay $100 to the user, adding that they deposited “$1000 in the Alliance bank to show our sincerity in the file.” When Ms. Carlill complained about the money, the company argued that the complaint should not be considered a serious and legally binding offer; instead, it was a “simple mess”; However, the Court of Appeal found that Carbolic had made a serious offer to a reasonable man and found that the reward was a contractual undertaking. All contracting parties must be able to agree and respect them as promised. Then comes the old rule that miners cannot enter into contracts. They are not considered mature enough to understand the effects of an agreement. Both parties must be of legal age and a healthy mind.
When a obligation comes into effect, contracts arise on the basis of a commitment from one of the parties. To be legally binding as a treaty, a promise must be exchanged for an appropriate consideration. There are two different theories or definitions of consideration: the theory of bargains of consideration and the theory of utility-detriment of consideration. Duress has been defined as a “threat of harm that is made to force a person to do something against his will or judgment; esp., an illegitimate threat made by one person to force a manifestation of another person`s apparent consent to a transaction without real will.  An example is Barton v Armstrong  in a person who has been threatened with death if he does not sign the treaty. An innocent party wishing to impose a contract of coercion on the person only has to prove that the threat was made and that it was one of the reasons for entering the contract; the burden of proof then rests with the other party to prove that the threat had no effect on the performance of the contract by the party. There may also be constraints on goods and sometimes “economic constraints.” A relationship of mutual agreement is neither legal nor binding for the parties, unless all of these factors exist.