Assert against

To be able to rely on a right, or on a fact about it, against someone who is not a party to it. Acquiring, losing or changing a right in rem (物権) in land or a building cannot be asserted against third parties until it is registered (登記) (Civil Code, Article 177), and a registered lease of land or a building can be asserted against a person who acquires a right in rem in it, such as a buyer, and against other third parties (Article 605). The Act on Land and Building Leases lets a tenant do without registering the lease itself: a right to use land for a building (借地権) can be asserted against third parties once the tenant owns a registered building on the land (Article 10, paragraph (1)), and a building lease takes effect against anyone who later acquires a right in rem in the building, such as a new owner, once the building has been handed over (Article 31). Some rules protect only a third party who did not know: a rescission for fraud cannot be asserted against a third party who did not know of the fraud and was not careless in not knowing (善意でかつ過失がない) (Civil Code, Article 96, paragraph (3)).