THE expression "zero tolerance" is normally applied to the style of policing famously promoted in New York three years ago by the then police commissioner, Bill Bratton.
But the expression refers to only one element of the strategies often credited with a dramatic fall in the city's crime levels.
The basis of the theory is that every time a minor offence is overlooked the offender and those who witness the offence being ignored by the authorities may be encouraged to more serious crime. Thus, a crackdown on minor offences should help to reduce the level of serious crime.
There are other perceived benefits: a reduction in petty or "street" crime should reduce public fear of crime, because minor offences are the sort most members of the public see. Police pressure on small time criminals may also encourage the offenders to pass on any information they, have about more serious crimes in an effort to avoid jail.
However, such policies cannot be pursued in isolation, merely by giving a new set of instructions to the police. Inevitably, a demand for extra policing means providing extra police. In New York, Bratton was allowed to add transit and housing officers to his police force, bringing the force to its highest ever level of 38,000 officers. Prisons were also expanded to ensure there were cells for the thousands of extra prisoners.
But "zero tolerance" New York style has its critics. While the targeted offenders were often street drug peddlers and muggers, officers also focused on the homeless living on the streets, and on drunks, beggars and "pests."
There were questions over the value of clearing the streets of such "nuisances" so that taxpayers, who were not genuinely threatened by them, could feel more comfortable. Ethnic groups also argued that they were unfairly targeted by the police.
During his term, Bratton was able to point to a significant cut in crime; the murder rate, for example, had dropped from 2,200 in 1990 to 1,200 by 1995. But critics said he paid too little attention to demographic changes which had worked in his favour. Academics said the key element in the fall in crime was a simultaneous reduction in the number of young men in the city. Most criminals are from this demographic group, and as a proportion of the population it was said to have peaked and started falling at about the same time the policing policies were initiated.
Bratton rejected this suggestion, saying the fall in crime occurred too quickly to have been purely the result of a demographic shift. Meanwhile, demographers say that in another 10 or 15 years the number of young men in New York will reach peak again, and the city will probably suffer a crime wave.
Asked last year if his New Yorkstyle policing could work in the Republic of Ireland, Bratton said it could. "Sure," he told The Irish Times. "It's replicable, it's transferable."
"Zero tolerance" can place a strain on relations between public and police, which is why many of its critics feel it could not work in the Republic. In most parts of the State gardai have a good relationship with the public. Gardai can use discretion and a "flexible" attitude towards minor offences as part of their overall effort to maintain law and order. Under "zero tolerance", such discretion could disappear.