¶ … Cause serves as the legal requirement for arrests and warrants. The Fourth Amendment bestows the:
right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation and particularly describing the place to be searched, and the persons or things to be seized."
Oath or affirmation" used in the Fourth Amendement limiting Warrant issue eludes to the fact that probable cause means there is reasonable certainty that a crime has already been committed and that a particular person is responsibe for that crime. Further, the requirements to describe the place to be searched, and the persons or things to be seized suggests that there should be facts that evidence of the crime will be discovered.
There is often a great deal of confusion between the concept of probable cause and reasonable suspicion. The easiest differentiation is that probable cause only deals with crimes that have been committed while reasoable suspicion can deal with crimes that have been or are about to be committed. Unlike probable cause, reasonable suspicion only requires reasonable belief as opposed to reasonable certainty. Thus, probable cause is supposed to be a stronger standard of evidence than reasonable suspicion. but, the difference between what constitutes reasonable certainty vs. reasonable belief is often highly subjective. In some instances of probable cause there is specific evidence of a crime such as fingerprints or evidence in plain view, but in other instances the context of a situation comes into play and this is where the line between probable cause and reasonable suspicion becomes blurred. For example, hearsay evidence or suspicious activity can support probable cause in instances where there are reliable sources or other evidence that increase the degree of certainty to legally allow a search or an arrest.
