Hansaria, J :- It is said that one swallow does not ordinarily make a summer. So also one prejudicial act cannot ordinarily form the basis of a preventive detention order. But there are exceptions to both the rules. In the present petition we are called upon to see as to what those exceptions are; and when can detention order be founded on a solitary instance of prejudicial activity.

2. Before adverting to this aspect, it may be stated that an order of detention is essentially a precautionary measure and is not a punishing device. In law there is a distinction between "prevention detention" and "punitive detention." This was highlighted by the Supreme Court in Francis Coralie, AIR 1981 SC 746: (1981 Cri LJ 306) A. K.Roy v. Union of India, AIR 1982 SC 710 : (1982 Cri LJ 340), where it has also said that "whatever smacks of punishment has to be scrupulously avoided in matters of preventive detention (See para 74)

3. It is true that the precautionary measure of detaining a person is based on a prognosis of the future behaviour of the person based on this past conduct. So, it is the past conduct on the basis of which the future pattern of behaviour is projected and preventive de