I believe by saying "the parties must agree in the same sense" the site means that they must have the same understanding of the contract. This is more commonly expressed by the phrase "a valid contract must be based on a meeting of minds". That is, if party A thinks the contract means one thing, and party B thinks it means something quite different, there is no valid contract at all.
For example, if A says 'I will sell you the Chevy for $1,000" and B accepts. A intended to sell the model Chevy displayed on nthe wall, B intended to buy the car in A's driveway. There is no meeting of minds, and thus no valid contract.
That site, in my view, has several examples of poor writing, and several errors of substance. I would be cautious in relying on it.
- "The parties to the agreement must have agreed about the subject matter of the agreement in the same sense and at the same time" The meaning is unclear.
- "*An agreement may be social agreement or legal agreement" Improper omission of articles.
- "it is necessary that the consent of parties to the contact must be free." Redundant. One of the boldface words should be removed.
- "According to Contract Act, a contract may be oral or in writing." Omission of required article.
- "But only those agreements which are enforceable in a court of law are contracts." Not correct. An agreement might, for example, be unenforceable for staleness, such as a debt that cannot be collected after a lapse of years, but it is still a contract.
- "Agreements of a social or domestic nature do not create legal relations and as such cannot give rise to a contract." Marriage is a valid and enforceable contract. So are domestic partnership contracts.
- "Consideration has been defined as the price paid by one party for the promise of the other." Consideration may be direct transfer of title and possession in an immediate sale, with no promise involved. Also, while most common-law countries hold to the rule that a valid contract requires consideration, many civil-law countries do not.
- "Thus, a contract entered into by a minor or by a lunatic is void." Contracts by minors are, in many but not all cases voidable, but they are not void just because one party is a minor.