The term illegal per se means that the act is inherently illegal. Thus, an act is illegal without extrinsic proof of any surrounding circumstances such as lack of scienter

Scienter

Scienter is a legal term that refers to intent or knowledge of wrongdoing. This means that an offending party has knowledge of the "wrongness" of an act or event prior to committing it. For example, if a man sells a car to his friend with brakes that do not work, and he does not know about the...

 (knowledge) or other defenses. Acts are made illegal per se by statute

Statute

A statute is a formal written enactment of a legislative authority that governs a state, city, or county. Typically, statutes command or prohibit something, or declare policy. The word is often used to distinguish law made by legislative bodies from case law, decided by courts, and regulations...

, constitution

Constitution

A constitution is a set of fundamental principles or established precedents according to which a state or other organization is governed. These rules together make up, i.e. constitute, what the entity is...

, or case law

Case law

In law, case law is the set of reported judicial decisions of selected appellate courts and other courts of first instance which make new interpretations of the law and, therefore, can be cited as precedents in a process known as stare decisis...

.

Drunk driving

Many drunk driving laws make driving with a blood alcohol content

Blood alcohol content

Blood alcohol content , also called blood alcohol concentration, blood ethanol concentration, or blood alcohol level is most commonly used as a metric of alcohol intoxication for legal or medical purposes....

 over a certain limit (such as 0.05% or 0.08%) an act which is illegal per se.

Antitrust

In the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, illegal per se often refers to categories of anti-competitive behavior

Anti-competitive practices

Anti-competitive practices are business or government practices that prevent or reduce competition in a market .- Anti-competitive practices :These can include:...

 in antitrust

Antitrust

The United States antitrust law is a body of laws that prohibits anti-competitive behavior and unfair business practices. Antitrust laws are intended to encourage competition in the marketplace. These competition laws make illegal certain practices deemed to hurt businesses or consumers or both,...

 law

Law

Law is a system of rules and guidelines which are enforced through social institutions to govern behavior, wherever possible. It shapes politics, economics and society in numerous ways and serves as a social mediator of relations between people. Contract law regulates everything from buying a bus...

 conclusively presumed to be an "unreasonable restraint on trade" and thus anti competitive. The United States Supreme Court has, in the past, determined activities such as price fixing

Price fixing

Price fixing is an agreement between participants on the same side in a market to buy or sell a product, service, or commodity only at a fixed price, or maintain the market conditions such that the price is maintained at a given level by controlling supply and demand...

, retail price maintenance, geographic market division, group boycott

Boycott

A boycott is an act of voluntarily abstaining from using, buying, or dealing with a person, organization, or country as an expression of protest, usually for political reasons...

s, and tying arrangements to be illegal per se regardless of the reasonableness of such actions. Traditionally, illegal per se anti-trust acts describe horizontal market

Horizontal market

A horizontal market is a market which meets a given need of a wide variety of industries, rather than a specific one.-Examples:In technology, horizontal markets consist of customers that share a common need that exists in many or all industries...

 arrangements among competitor

Competition (economics)

Competition in economics is a term that encompasses the notion of individuals and firms striving for a greater share of a market to sell or buy goods and services...

s.

The illegal per se category can trace its origins in the 1899 Supreme Court case Drystone Pipe & Steel Co. v. U. S., 175 U.S. 211

Case citation

Case citation is the system used in many countries to identify the decisions in past court cases, either in special series of books called reporters or law reports, or in a 'neutral' form which will identify a decision wherever it was reported...

 (1899).

A number of cases have subsequently raised doubts about the validity of the illegal per se rule. Under modern Antitrust theories, the traditionally illegal per se categories create more of a presumption

Presumption

In the law of evidence, a presumption of a particular fact can be made without the aid of proof in some situations. The types of presumption includes a rebuttable discretionary presumption, a rebuttable mandatory presumption, and an irrebuttable or conclusive presumption. The invocation of a...

 of unreasonableness. The court carefully narrowed the per se treatment and began issuing guidelines. Courts and agencies seeking to apply the per se rule 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 broadening per se treatment to new or innovative business relationships.

See also

• Negligence per se
  Negligence per se
  Negligence per se is the legal doctrine whereby an act is considered negligent because it violates a statute . In order to prove negligence per se, the plaintiff must show that# the defendant violated the statute,...
  
  
• Malum in se
  Malum in se
  Malum in se is a Latin phrase meaning wrong or evil in itself. The phrase is used to refer to conduct assessed as sinful or inherently wrong by nature, independent of regulations governing the conduct...
  
  
• Rule of reason
  Rule of reason
  The Rule of Reason is a doctrine developed by the United States Supreme Court in its interpretation of the Sherman Antitrust Act. The rule, stated and applied in the case of Standard Oil Co. of New Jersey v. United States, 221 U.S...
  
  
• Strict liability
  Strict liability
  In law, strict liability is a standard for liability which may exist in either a criminal or civil context. A rule specifying strict liability makes a person legally responsible for the damage and loss caused by his or her acts and omissions regardless of culpability...