The agreement between Titus and Caius is enforceable This type of agreement is a contractus innominate which is a common agreement that falls outside of the main 8 contracts This can be specified as an exchange agreement party A gives party B something in return for something else This contract was presumably made by stipulation as it is the only way to make the agreement an enforceable deed We can also assume that the contract is based on bona fides good faith of both parties The stipulation is a very specific formulation to validate agreements It consists of a question with the specifics and an answer that answers the question exactly Titus should therefore initiate litigation per formula rei vindictio vindication Per Formulam is a two stages procedure introduced to increase efficiency and facilitate from the former one Legis actionem First stage in iure two parties appear in front of praetor and present their case and the praetor would fill in a standardized formula