This concept has been defined as an obligation to reach an agreement or to negotiate with a view to reaching an agreement. This obligation may arise from a treaty and whether the parties are legally bound by the treaty to conclude a further agreement on a specific point will depend on an interpretation of the words used in the treaty. Vague or indeterminate language may indicate that the obligation to negotiate is political rather than legal. If the source of the obligation is clearly established, the pactum may create certain procedural obligations concerning a subsequent agreement. These obligations may need to be fulfilled immediately, or at a later date.
Writers differ about the legal obligations arising from each pactum .
In a pactum de negotiando the obligation is to negotiate in good faith with a view to concluding an agreement, whereas in a pactum de contrahendo the obligation may be more extensive and may require the parties to reach an actual permanent agreement. The judicial elaboration of pacta has indicated specific duties for the parties. The latter can be assessed through objective criteria, by examining the summary of the negotiations, including diplomatic exchanges, formal conference negotiations, exchange of notes disclosing each party's views and direct negotiations through foreign ministers. Good faith can also be evaluated by examining whether the parties have regard for the procedures, show a willingness to consider promptly adverse proposals or interests, and are diligent in the negotiations. Bad faith may not be presumed, but will need to be proved by the party alleging it and be based on unjustifiably breaking off negotiations, abnormal delays, disregard for agreed procedures or systematic refusal to take into consideration adverse proposals or interests.