Single-subject rule

The single-subject rule is a rule in the constitutional law of some jurisdictions that stipulates that some or all types of legislation may deal with only one main issue. One purpose is to avoid complexity in laws, to avoid any hidden consequences that legislators or voters may miss when reading the proposed law. Another is to prevent legislators attaching an unpopular provision ("rider") to an unrelated popular one, whether in the hope of sneaking the unpopular one through, or in the hope of causing the popular one to be rejected (a type of wrecking amendment).

In English law, the long title of a bill or act of parliament states its purpose; this may enumerate multiple purposes, or end with a vague formula like "and for other purposes". A proposed amendment to a bill may be rejected if it is outside the scope defined in its long title; alternatively, the title may be amended to increase its scope. An omnibus bill covers a number of diverse or unrelated topics.

The single subject rule exists in 41 state constitutions in the United States of America.

For example, the constitution of Minnesota, Article IV, Section 17, requires that "No law shall embrace more than one subject, which shall be expressed in its title." Conversely, neither the U.S. Congress nor the U.S. Constitution has such a rule so riders which are completely unrelated to the main bill are commonplace. These amendments are often put into bills at the last minute, so that any representative who may read the legislation before actually voting on it will not have a chance to catch it. An effort is underway, however, to add a single subject amendment to the U.S. Constitution to apply a single subject rule to the Congress.

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