Civil decretum systems take the approach that an exchange of promises, or a concurrence of wills alone, rather than an exchange in valuable rights is the correct basis. So if you promised to give me a book, and I accepted your offer without giving anything in return, I would have a granted right to the book and you could not about-face your brain about giving me it as a gift. However, in daily law systems the brain wave of culpa in contrahendo, a form of 'estoppel', is increasingly disposed to create obligations during pre-contractual negotiations. Estoppel is an equitable doctrine that provides for the nativity of legal obligations if a party has given another an assurance and the other beat relied on the assurance to his detriment. A integer of commentators have suggested that consideration be abandoned, and estoppel be absorbed to replace it as a basis for contracts. However, legislation, rather than judicial development, also-ran been touted as the only means to remove this entrenched frequent behest doctrine. Lord Justice Denning famously stated that "The California Contract Warehouse doctrine of consideration is too firmly fixed to be overthrown by a side-wind."
A guarantee is an shift of promises between two or extra parties to do, or refrain from doing, an act which is enforceable in a court of law. It is a binding enforceable agreement. That is to say, a evidence is an exchange of promises for the breach of which the law will provide a remedy.