Solve et repete - Respect your obligation first, then you can ask for reimbursement. Used in those situations in which one of the two (or more) parties needs to complete his obligation before being allowed to ask for the opposite obligation to be respected by his counter party. Usually this principle is used in fields and subjects in which a certain general steadiness or uniformity of the system has been considered a relevant value by the legislator. The case is typical of service contracts with repeated obligations (like with gas, water, electricity providers and similars), in which irregularities on one side cannot be balanced if not in a regular situation (i.e., of payments) on the other side. The customer, for example, might be asked to pay regularly the new bill, before contesting the previous one in which he found irregular calculations, and asking for a balancement with newer bills; he thus cannot by himself determine a discount in the next payment.⏎
Volenti non fit injuria - "Injury is not done to the willing." Notion that a person cannot bring a claim against another for injury, if said person willingly placed themselves in a situation where they knew injury could result.⏎
Ubi lex voluit, dixit; ubi noluit, tacuit - When the law wanted to regulate the matter in further detail, it did regulate the matter; when it did not want to regulate the matter in further detail, it remained silent (in the interpretation of a law, an excessively expansive interpretation might perhaps go beyond the intention of the legislator, thus we must adhere to what is in the text of the law and draw no material consequences from the law's silence).⏎
Rex non potest peccare - "The king can do no wrong." Used to describe the basis for sovereign immunity.⏎