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).⏎
Res inter alios acta vel iudicata, aliis nec nocet nec prodocet - What has been agreed/decided between people (a specific group) can neither benefit nor harm a third party (meaning: two or more people cannot agree amongst each other to establish an obligation for a third party who was not involved in the negotiation; furthermore, any benefit that may be established will have to be accepted by the third party before it can be implemented).⏎
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.⏎
Ultra posse nemo obligatur - "No one is obligated (to do) more than he can." Specifies that one should do what he can to support the community, but since everyone has different levels of ability, it cannot be expected that all will perform the same.⏎