Grandfather clause

In the U.S, a grandfather clause is an exception which allows something pre-existing to remain as it is, despite a change to the contrary in the rules applied to newer situations. It is often used as the verb "to grandfather" or "grandfather in", or alternatively as "grandfathering clause". Often, such a provision is used as a compromise, to effect new rules without upsetting a well-established physical or political situation.

Some examples:

• The international trade in slaves through 1808 was grandfathered into the United States Constitution.
• Fire sprinklers are required in all new buildings – but due to the great expense of having older ones retrofitted, they are generally exempt unless and until they are renovated. Such an exception proved deadly to 100 people in 2003 at The Station nightclub fire in Rhode Island, and gutted a large a large part of an older high-rise office building in the Peachtree 25th fire in Atlanta in 1989.
• Zoning laws often grandfather in existing buildings or other uses, such as when an area is rezoned from residential to commercial, and the existing home on the lot need not be torn down or converted.
• Existing toll roads were allowed to become part of the Interstate highway system in the U.S, even though no new Interstates can have tolls.
• Early Internet RFCs which were de facto standards were grandfathered into the official IETF Internet standard process.

The original grandfather clauses were in laws from 1895 to 1910 in seven of the southern U.S. states as a Jim Crow law, in order to prevent blacks from voting. These laws provided that anyone allowed to vote before the American Civil War, and any of their descendants, were exempt from poll taxes levied and/or supposed "literacy" tests required at the time. Since the Fifteenth Amendment, granting former slaves the right to vote was not ratified until 1870, this disenfranchised blacks, but not whites. They were later declared unconstitutional.