What is "probable cause"?

Question

I know what probable cause is and how it is used in law/law enforcement. But what does the actual term "probable cause" mean?

In a sentence where it is used like

"The drug dog's alert gave me probable cause to search your vehicle"

in this case the officer has "definite cause" why is probable used?

In the wikipedia definition it says:

"Probable" in this case may relate to statistical probability or to a general standard of common behavior and customs

https://en.wikipedia.org/wiki/Probable_cause

But that is also very vague, "statistical probability" or "general standard" of what? Statistical probability of, in the given example, having drugs? How does that relate to giving cause?

It just seems like any way you try to interpret the word "probable" it doesn't make sense, you either have cause to search/arrest/etc. or you don't where is the probability?

Answer 1

...in this case the officer has "definite cause." Why is probable used?

"Probable cause" is a standard for when a property search can be conducted or a warrant issued. According to the Wikipedia article you linked to, Ballentine's Law Dictionary defines probable cause as

a reasonable amount of suspicion, supported by circumstances sufficiently strong to justify a prudent and cautious person's belief that certain facts are probably true

We do not talk about "definite cause" because there is no such legal standard. Having "definite cause" as you suggest here simply means you have a very strong case to satisfy the legal standard of probable cause. Referring to the above definition, the officer whose drug-sniffing dog alerts at a traffic stop certainly has a "reasonable amount of suspicion." The officer may actually have an incredibly high amount of suspicion, but that's irrelevant to the probable cause standard. It is merely sufficient that the officer's level of suspicion is "reasonable" and backed by suitable evidentiary circumstances.

It just seems like any way you try to interpret the word "probable" it doesn't make sense, you either have cause to search/arrest/etc. or you don't where is the probability?

The probable cause standard is "probable" because it does not impose exacting requirements on law enforcement. (Note that the U.S. Constitution uses "probable" slightly differently from its modern meaning; see another answer.) It need not be blatantly obvious that a crime is being committed but likely that a crime is being committed. Of course, the exact standard of how likely is likely enough to satisfy the standard of probable cause (and what evidence constitutes a particular threshold of likelihood) is a test for the court to determine.

Answer 2

To amplify on apsiller's answer, this is an instance of a subtle shift in word connotations over the centuries. These days, "probable" has taken on a meaning closer to "likely", which is related to frequency of occurrence and is more strongly associated with statistical analysis. Earlier, it was more closely related to "proof" as in "burden of proof".

Answer 3

Check out Brineger v US (1949):

Probable cause exists where the facts and circumstances within the officers' knowledge, and of which they have reasonably trustworthy information, are sufficient in themselves to warrant a belief by a man of reasonable caution that a crime is being committed.

This is different than reasonable suspicion which is elucidated in Terry v Ohio (1968):

The term "probable cause" rings a bell of certainty that is not sounded by phrases such as "reasonable suspicion."

[T]he police officer must be able to point to specific and articulable facts which, taken together with rational inferences from those facts, reasonably warrant that intrusion.