Illegalper se

InUS law,the termillegalper semeans that the act is inherently illegal. Thus, an act is illegal without extrinsic proof of any surrounding circumstances such as lack ofscienter(knowledge) or other defenses. Acts are made illegalper sebystatute,constitutionorcase law.

Drunk driving

Manydrunk drivinglaws make driving with ablood alcohol contentover a certain limit (such as 0.05% or 0.08%) an act which is illegalper se.

Antitrust

In theUnited States,illegalper seoften refers to categories ofanti-competitive behaviorinantitrustlawconclusively presumed to be an "unreasonable restraint on trade" and thus anti competitive. TheUnited States Supreme Courthas, in the past, determined activities such asprice fixing,geographicmarket division,andgroup boycottto be illegalper seregardless of the reasonableness of such actions. Traditionally, illegalper seanti-trust acts describehorizontal marketarrangements amongcompetitors.

The illegalper secategory can trace its origins in the 1898 Supreme Court caseAddyston Pipe & Steel Co. v. U.S.,175 U.S. 211(1898).

A number of cases have subsequently raised doubts about the validity of the illegalper serule. Under modern Antitrust theories, the traditionally illegalper secategories create more of apresumptionof unreasonableness.The court carefully narrowed theper setreatment and began issuing guidelines. Courts and agencies seeking to apply theper serule must:

1. show "the practice facially appears to be one that would always or almost always tend to restrict competition and decrease output";
2. show that the practice is not "one designed to 'increase economic efficiency and render markets more, rather than less, competitive'";
3. carefully examine market conditions; and
4. absent good evidence of competitiveness behavior, avoid broadeningper setreatment to new or innovative business relationships.

See also

• Malum in se
• Negligenceper se
• Presumption
• Rule of reason
• Strict liability (criminal)