The debate about "dangerous dogs" cannot progress without clarification of the meaning of "dangerous." A thing, activity, dog or person should be considered "dangerous" if it or he presents an unacceptably high risk of serious injury, even before causing harm. This definition uses the word "risk." Cars, plastic bags, electrical cords and other mundane objects are considered dangerous to some degree because of their potential for harm, not their individual history of crashing, suffocating or electrocuting. When discussing whether a dog is "dangerous" in this sense, the issue is not whether that particular dog will ever bite, but whether it presents too great a risk of serious injury -- not because of what it has done, but because of what others of its class have done. The definition also uses the term "serious injury." The bites of teacup-sized dogs and even herding dogs (who use their mouths to seize and guide as opposed to crush and rip) do not present the risk of serious injury inherent in the bites of dogs which were bred for the specific purpose of killing animals. When "dangerous" is defined in this way, many believe that it accurately describes the latter group of dogs.

Let us turn exclusively to the legal meaning of "dangerous dog." A dog can be legally classified as "dangerous" or "vicious" based upon its actions, its breed, or the actions of its owner, either before or after an official hearing, pursuant to the law of the jurisdiction where the dog is present. A dog classified as "dangerous" or "vicious" is subject to being confined or kept pursuant to strict rules, and might even be euthanized, and its owner can be fined, jailed and ordered to do or not do things in the future that pertain to animals.

This type of law is referred to generically as the "dangerous dog law," and usually is found in the municipal or county code, but often is part of the state code. Additionally, there may be state court decisions that have become part of the "dangerous dog law." Furthermore, the regulations of the local authorities, such as the city's animal control department, are an essential ingredient to the dangerous dog law, even though they technically may not be part of the law itself.

The law often makes a distinction between the words "dangerous" and "vicious." When both words are used, "dangerous" usually refers to the risk of harm by any action of the dog, whether or not benign, such as biting, jumping, slamming against, grabbing, swiping with its paws, and over-friendliness that is expressed as jumping upon. For example, a dog that has the habit of running to a person and jumping enthusiastically upon him could be considered dangerous because of the risk of harm to an elderly pedestrian. Attorney Kenneth Phillips also has contended that a dog's propensity to chase and fight with other domestic animals should be considered dangerous to people because of the high number of serious injuries to people that occur during such incidents. (See "A propensity to attack other dogs means a dog is dangerous to people," in Dangerous and Vicious Dogs.) The term "vicious" refers to a dog that has done or communicated by its actions an intention, habit, tendency or propensity to do something harmful to people. For example, a dog that has a habit of jumping upon people might be considered dangerous but not vicious.

The basis for classifying a dog as "dangerous" or "vicious" differs from one jurisdiction to the next. All jurisdictions are interested in eliminating that which poses unacceptable risk, but from place to place the focus of the "dangerous dog law" can be the actions of a particular dog, its breed, or the acts or omissions of its owner. In some jurisdictions, for example, a dog that threatens a person but does not inflict actual physical injuries is classified as dangerous, whereas in other places it is not. In some places, a dog is regarded as dangerous if the owner of the dog has violated certain animal control rules more than a given number of times. In a sense, the owner is actually the dangerous one, and the dog's confinement or existence is regulated not because of the dog's behavior but because of its potential to create harm in the hands of that particular owner. Also, as noted above, several nations and American cities classify certain breeds as "dangerous" simply on the basis of breed, and regardless of any particular dog's disposition, temperament or behavior.

In conclusion, although we may feel that we know a dangerous dog when we see one, it turns out that dangerousness is a political and controversial topic, and the laws about it are confusing and contradictory.