to pass legislation, a majority of the members of a legislature must vote for a bill (proposed law) in each house. normally there will be several readings and amendments proposed by the different political factions. if a country has an entrenched constitution, a special majority for changes to the constitution may be required, making changes to the law more difficult. a government usually leads the process, which can be formed from members of parliament (e.g. the uk or germany). however, in a presidential system, the government is usually formed by an executive and his or her appointed cabinet officials (e.g. the united states or brazil).