In some circumstances, these terms are used differently. For example, in English insurance law, an insured`s breach of a “condition precedent” is a total defence against the payment of duties. :160 In general insurance law, a guarantee is a promise that must be kept.  With respect to product transactions, warranties promise that the product will continue to operate for a certain period of time. There are laws that protect consumers from unfair contract terms when they have had little or no opportunity to negotiate with companies (e.g. B model contracts). These rules apply subject to agreements to the contrary. The consideration contained in the contracts is an essential element in the constitution of a valid contract and relates to what each of the parties concerned derives from the agreement.