●  The terms of an agreement must be sufficiently certain or the agreement will be void for uncertainty. Agreements for the parties to agree a matter, such as the price, will generally lack the necessary certainty. However, if nothing is said about the price, in some circumstances statute may imply a reasonable price.

●  If there is uncertainty so that no contract results, in some circumstances there may nevertheless be an obligation to pay the reasonable value for requested performance (a quantum meruit).

●  An agreement mistake will occur where one or both of the parties allege that they made a fundamental mistake as to a term which prevents agreement. Such a mistake means the contract is void. Alternatively, a contract may be voidable for a mistake as to attributes and this protects innocent third parties who have acquired the contract goods.

●  It may be possible to rectify a written record of an agreement where there is a transcription mistake in recording that agreement accurately. The plea of non est factum (‘this is not my deed’) may very rarely be available where it is claimed that a signed document has been signed by mistake because the document is fundamentally different in nature to the document believed to have been signed.