"Reasonable and probable cause" is the lowest standard of proof under common law. Although this standard is used for many purposes, it's primary uses are:
- To determine if there is sufficient evidence to issue a search warrant; and
- To determine if there is sufficient evidence to issue an indictment for a serious crime.
Although this standard is important in criminal law, it also has many applications in civil law and administrative law as well.
The standard can be most easily explained by examining its two parts:
Reasonable[]
In order to meet this part of the standard, there must be some evidence that would normally be acceptable in a court of law that supports the outcome to be reached. Mere suspicion, supposition or conjecture is insufficient to meet the standard. Moreover, particularly in ex parte applications, the party seeking relief is expected to disclose any evidence that may not support the conclusion. In the end, the court official must be able to accept that on the balance of the evidence presented that there is at least a hope that the order granted will result in a successful conclusion.
Probable[]
It is not necessary to prove it is more likely than not that the evidence leads to the conclusion sought. However, it is required to show that, based on the evidence presented, there is at least a very good chance that the search or prosecution will be successful. It is not enough that success is merely "possible", it must be "likely".
See also prima facie evidence - evidence that often leads to reasonable and probable cause.