This type of marriage contract is drafted prior to a marriage to define ownership of property and assets brought to the marriage by each party. Asking your partner to sign a prenup is not signaling your expectation that the marriage will fail; it is a document that can be used to avoid costly and adversarial negotiations if a divorce becomes a reality. In fact, many stipulations can be built into a prenuptial agreement such as the fact that the document expires after 15 years of marriage.
Post-nuptial agreements can be written at any time during the marriage. This document serves to define the ownership of property or assets acquired while married. If homes, cars, boats or other assets are gained throughout the marriage, a post-nuptial agreement can be created to explain who owns what. These documents can be helpful for driving a dispute to a speedy and effective conclusion if the parties decide to divorce.
Again, the stigma attached to pre- or post-nuptial agreements is undeserved. There are a whole host of different reasons to have them drafted. Merely drafting this type of agreement is not an admission that you expect the marriage to fail, but it is a way to keep assets organized and minimize the time spent in mediation if a divorce becomes a reality.