The term consensual does not mean that the consent of the parties is more emphatically given than in other forms of agreement, but it indicates that the obligation is annexed at once to the consensus, in the contracts of this type.
[2] Justinian's Institutes classify the following contracts as ex consensu: emptio venditio, locatio conductio, societas and mandatum.
The seller in a contract of sale had to guarantee the buyer free, undisturbed and lawful possession of the thing sold, and to secure him against latent faults.
The contract of sale is completed by the consent of the parties; after this, the thing sold is at the risk of the buyer, who also obtained the advantage of any increase to the object.
If the seller disposed of a thing that was not in commercio, such as a temple or a religious place, he was liable to the buyer for any loss that the latter might have incurred by the error.
If the price was less than half the value of the thing sold, the seller might rescind the contract unless the buyer agreed to make up the deficiency.
If the object sold was totally unfit for the purpose intended, the buyer might bring an action for rescission – the actio redhibitoria.
If the object possessed some defect which diminished its value, the buyer could bring the actio quanti minoris within one year; by this he obtained a corresponding reduction in price.
[9]For example, by English law, the sale of a specific movable is a conveyance and transfers the right in rem.
The locatio conductio might be: In the case of leased land, the landlord could take farm implements and other property of the tenant by the actio Serviana.
The remedy between partners was the actio pro socio, for all cases which did not fall within the actions, such as those furti, vi bonorum raptorum, etc.
The execution of a mandatum was the gratuitous performance of an act for another, the rights of both the mandator ('principal') and the mandatary ('agent') being amply protected by the praetors.