TOTALITY OF THE CIRCUMSTANCES
The law operates with two major substantive standards:
"Bright line" and "Totality of the circumstances"
A totality of the circumstances standard suggests that there is no single deciding factor, that one must consider all the facts, the context, and conclude from the whole picture whether there is probable cause, or whether an alleged detention is really a detention, or whether a citizen acted under color of law. The primary guide for this kind of substantive rule is the fact patterns from cases in which the courts have found that the criteria were met.
A bright line rule, on the other hand, gives specific guidelines. Any unwanted, non-accidental touching of the person of another constitutes a battery. That's it. Police may not enter property on which they do not have a right to be without a warrant or other special legal justification. They enter. Violation. The line is clear cut.
Why not make all our laws bright line and avoid the problems of trying to decide these complex contextual issues? Because human experience is infinitely varied, and we cannot write adequate laws to cover all possible circumstances. Also, we need our police to have some discretion in enforcing the law. If they were completely hemmed in by bright line rules, they would be unable to act when we need them. But in giving them discretion, we risk abuse of discretion. That is an eternal problem of humankind. As the crime rate rises, we give police more discretion. As police excesses grow in a time of relative low crime, we take away discretion and give more bright line rules.
Probable cause and reasonable cause are judged by a totality of the circumstances standard. That means you have to take all the facts into consideration and weigh them. There is no single definition of what gives probable or reasonable cause. Why? So police will have the necessary flexibility to meet the myriad different situations that occur. ( http://www.csudh.edu/dearhabermas/totcirc.htm