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Departments : Point of Law

Probable Cause and Reasonable Suspicion

These familiar terms are often confused and misused.

June 07, 2011  |  by Devallis Rutledge - Also by this author


Some actions you take have been classified by Supreme Court decisions as requiring that you articulate a "reasonable suspicion" in order to make them constitutionally reasonable, while others can be undertaken only if there is "probable cause" ("PC"). But what do these terms mean? And how do you match the right level of justification with the kind of conduct you're seeking to justify?

Probable Cause

The Fourth Amendment provides that "no warrants shall issue, but upon probable cause." The Constitution doesn't furnish any definition of "probable cause," leaving that task to the Supreme Court, which has also applied the probable cause standard to certain warrantless activities.

The term "reasonable suspicion" is not of constitutional derivation but was fashioned by the court to describe a level of suspicion lower than probable cause. The court has struggled to provide meaningful definitions of both terms, and law enforcement officers have likewise struggled to understand and apply the court's vague, general pronouncements. In Ornelas v. U.S., the court acknowledged the problem:

"Articulating precisely what 'reasonable suspicion' and 'probable cause' mean is not possible. They are commonsense, non-technical conceptions that deal with the factual and practical considerations of everyday life on which reasonable and prudent men, not legal technicians, act. As such, the standards are not readily, or even usefully, reduced to a neat set of legal rules." (Ornelas v. U.S.)

Though it may not be possible to articulate precisely what "probable cause" means, the court has offered this guidance:

"Probable cause does not require the same type of specific evidence of each element of the offense as would be needed to support a conviction." (Adams v. Williams)

"Finely-tuned standards, such as proof beyond a reasonable doubt or by a preponderance of the evidence, useful in formal trials, have no place in the probable cause decision." (Maryland v. Pringle)

"The rule of probable cause is a practical, non-technical conception affording the best compromise that has been found for accommodating often opposing interests." (Beck v. Ohio)

"The process does not deal with hard certainties, but with probabilities. Long before the law of probabilities was articulated as such, practical people formulated certain commonsense conclusions about human behavior; jurors as fact-finders are permitted to do the same-and so are law enforcement officers." (U.S. v. Cortez)

"We have held that probable cause means a 'fair probability'." (U.S. v. Sokolow)

Give up? Sometimes, it's easier to define something by pointing to a category of examples that make the meaning clear. For instance, coming up with an abstract definition of "red" might be difficult, but the meaning could be made clear by saying, "It's the color of delicious apples, blood, ripe strawberries and tomatoes, ketchup, and stop signs."

Similarly, it may be easier to get a handle on the concept of "probable cause" by identifying familiar law enforcement activities associated with a requirement of PC. As the Fourth Amendment mandates, you need PC to get a search warrant.

The same goes for arrests. "Whether an arrest is valid depends upon whether, at the moment the arrest was made, the officers had probable cause to make it-whether at that moment the facts and circumstances within their knowledge and of which they had reasonably trustworthy information were sufficient to warrant a prudent man in believing that the person to be arrested had committed or was committing an offense." (Beck v. Ohio)

And PC is the level of information and suspicion that justifies the warrantless search of "fleeting targets," such as cars, trucks, buses, trains, airplanes, and boats. (U.S. v. Ross)

There is also a concept that is sometimes referred to as "probable cause plus." In Winston v. Lee, the Supreme Court said that when a search involves highly invasive probes into the body-such as surgery to recover a bullet-there must be probable cause to believe evidence will be found, plus a compelling need for the evidence that outweighs the suspect's right to be free of invasive procedures that could threaten his life or health.

Reasonable Suspicion

It was not until 1968 that the need for a standard lower than PC was recognized by the Supreme Court. In Terry v. Ohio, the court confronted defense challenges to both the detention of a robbery suspect and the weapons frisk that disclosed the gun he sought to suppress. The court noted that a temporary investigative detention is less of an infringement of a person's liberty than arresting him and taking him into custody. Therefore, said the court, police need not have as much justification for this lower level of restraint as the probable cause that would have been required to make an arrest. The court called this lower justification standard for detentions "reasonable suspicion."

This discussion shows why it is a mistake to use the expression "PC for the stop," which mismatches a higher level of justification with a lower level of infringement of individual liberty. "In Terry v. Ohio, we held that the police can stop and briefly detain a person for investigative purposes if the officer has a reasonable suspicion supported by articulable facts that criminal activity is afoot, even if the officer lacks probable cause." (U.S. v. Sokolow)

As for the weapons pat-down search of Terry, the court recognized that an officer-safety search limited to a frisk of a suspect's outer clothing is less of an intrusion on the suspect's privacy than a full-scale search of everything he was wearing and carrying; this partial search could be justified, said the court, based on a reasonable suspicion that the person might be armed and dangerous, which would be less than the PC necessary for a thorough search.

As with the concept of "probable cause," the lower standard of "reasonable suspicion" was not easily defined. "The concept of reasonable suspicion, like probable cause, is not readily or even usefully reduced to a neat set of legal rules," but "the level of suspicion required for a Terry stop is obviously less demanding than that for probable cause." (U.S. v. Sokolow)

The court has said that both the quantity and the quality of information constituting reasonable suspicion may be below the level needed for PC. "Reasonable suspicion is a less demanding standard than probable cause not only in the sense that reasonable suspicion can be established with information that is different in quantity or content than that required to establish probable cause, but also in the sense that reasonable suspicion can arise from information that is less reliable than that required to show probable cause." (Alabama v. White)

Again, defining reasonable suspicion in terms of familiar activities, it is the level of information and suspicion you need when you make a vehicle stop or a pedestrian stop, or pat down someone who might be armed, or search a vehicle based on reasons to believe it may harbor concealed weapons. (Michigan v. Long)

In a Nutshell

"Probable cause" means reasonably reliable information to suspect there is a "fair probability" that a person has committed a crime, or that a search will reveal contraband or evidence. "Reasonable suspicion" is a strong suspicion, even if based on less information of a less-reliable nature, that a person is involved in criminal activity or may be armed and dangerous.

Devallis Rutledge is a former police officer and veteran prosecutor who currently serves as Special Counsel to the Los Angeles County District Attorney. He is the author of 12 books, including "Investigative Constitutional Law."

Comments (20)

Displaying 1 - 20 of 20

Mike Glenn @ 7/2/2012 1:19 PM

I find this story extremely Informative In helping someone fully understand he 2 terms at hand. " Example": I have reasonable suspicion and probable cause to believe that obama care will wreck and bankrupt the healthcare industry!

Philip @ 5/4/2013 3:07 AM

oh, how we play with words here to establish a fluidity to legal discourse which translates at street/home/work level to no solid expectation of dearly-bought rights. If you're out late at night not breaking any laws and a cop approaches with a demand to show ID or face arrest, your only choice in Nazi America is to surrender your rights. And it goes way downhill from there.

Yu @ 9/8/2013 1:19 AM

so well written!

R413 @ 9/22/2013 12:37 PM

I'm joing this discussion late as I am reading past articles to identify case law relating to an ong

Honor Shield @ 10/14/2013 11:15 AM

That is pretty cynical. We are not in any stretch of any reasonably sane mind in a Nazi America. You need to read your history well and note the stark differences and stop loosely throwing false accusations around. I am glad the law gives an officer the right to check out somebody cruising the streets at night or hanging out at night. This has been clearly established over and over again and articulated in many instances that started with reasonable suspicion and led to an arrest of burglars, drive by killers, gangsters, criminals of every variety. It's a well known and established pattern that the nefarious among us use the cover of night to continue their harmful activities and predatory practices. I would only hope that officers never shy away from honing the skills necessary to keep using their reasonable suspicion (which includes the time of day or area and behavior on seeing an officer) to stop and check what's going on. If the officer was mistaken then the law allows him to be.

Honor Shield @ 10/14/2013 11:30 AM

Thank you for the excellent article worth it's weight in gold Mr. Devallis Rutledge may God bless you every day.

JEFF HAIRE @ 12/10/2013 3:44 PM

This Police Magazine article is one of the best and most concise summaries of the distinctions between two commonly misunderstood legal terms of critical importance in police report writing.

Glenn @ 5/19/2015 8:46 AM

Here is my issue with this entire concept. If no legal definition of Probable Cause exists, then how can you make a new definition of a new word based upon an abstract idea to start with? It is like me claiming that a a-bomb-in-a-bull actually does not mean anything, but I am going to base aboninabull off the what a-bomb-in-a-bull mean, and then claim that using the lesser idea it must them be true. That is what I am getting out of this entire article.

dan @ 5/28/2015 2:38 PM

The article MISREPRESENTS the the two elements of Amendment 4. First, there is no such element as "reasonable suspicion"--It is REASONABLE SEARCH.

The word REASONABLE deals ONLY with the "SEARCH" aspect and not the suspicion aspect.

1785 dictionary of common use defines “PRO'BABLE. Likely; having more evidence than the contrary.” That means that in order to get the warrant--there MUST be more evidence to support a CONVICTION than to support the innocence.

From the same dictionary, “URE'ASONABLE. 1. Exorbitant ; claiming or insisting on more than is fit. 2. Not agreeable to reason. 3. Greater than is fit ; immoderate.”

If you and/or your vehicle is NOT the SUSPECT of a crime--IT IS UNREASONABLE for the government Officer to pull you over to question or search you or your vehicle whether at a DUI or INLAND "border" checkpoints.

bill @ 6/28/2015 11:22 PM

If the police stop you for a traffic violation..find a gun and drugs in the car...make an arrest on those charges...but fail to issue a ticket for the traffic violation will the evidence be supressed at court?

Brad @ 9/9/2015 10:20 AM

Maybe. The courts have stated that a simple traffic violation is not "probable cause" that any crime has been committed being worthy of a vehicle search. However: Did you give the *permission* to search the car? Did they observe something else during the stop to give them probable cause? A police dog may be called to sniff drugs under "Reasonable Suspicion" - and if the dog alerts, that would be "Probable Cause".

Dj @ 10/23/2015 9:26 PM

I was stopped for supposed no turn signal and denied having any drugs but the vehicle was a friends that had not transferred tags yet. I was told to step out but was not told i was being detained or arrested. The officer told me to put my hands on the vehicle and i knew he was going to search me so i did not comply because i fealt he did not have prob cause. So i then tried to discard or eat my evidence but was forcibly grabbed and searched anyway. Was this really cause to search me when they had no evidence or warrant to support telling me to comply in the first place?

Dj @ 10/23/2015 9:31 PM

I was pulled over and did not concent to a search for supposed no turn signal n plates that had not been transferred yet. I stepped out but did not feel i had to comply with being searched so i resisted and was forcibly searched and found with drugs. Does the plates give probable cause to search my person wasnt told i was being detained n denied having anything but was told to put my hands on the vehicle so i tried to eat it and was wrestled till i dropped it and was then detained and read my rights. Does this sound probable or legal?

Kristin Porter @ 11/8/2015 1:24 AM

I was driving around 12 am and a cop was bright lighting me so I turned on my brights.The cop immediately turned around and followed me for a bit then attempted to pull me over. Did not have license on the car yet,..In the police report the cop said my dim passenger side headlight was out...I have 5 witnesses that have seen the lights and will swear the light is working...will I beat the probable cause?

Smoke @ 11/15/2015 2:55 AM

Let's say your phone comes up missing or stolen and then winds up being @ the scene of a crime?....What do you do?

Darious Porter @ 2/11/2016 2:39 PM

DJ, lol, if you try and destroy drugs in front of a cop.. you are committing a felony. If you are found with drugs its usually only a misdemeanor. If you are trying to swallow a felony amount of drugs, in front of a cop or not, you'll likely die depending on the drug. No plates is a crime not a moving violation. You get a criminal ticket, not a traffic ticket. The cop then has the right to pat you down for weapons, if you reach for your hidden drugs (while the cop is making sure he isn't going to get shot or stabbed) then yah... you are boned.

Jedi @ 8/18/2016 10:38 PM

I picked up a friend. Started driving away. Halfway den st my friend said Nevamind bring me back my girls coming to get me. So I turn into driveway n bring him back dropping him cross the st from pickup spot. I pull away to head home n unmarked lights me up and few marked cars come from multiple angles. Wasn't in a high drug traffic area and officer even said in report he didn't see hand to hand or any sketchy transaction. Just that is 29 yrs experience blablabla I believe it was a terry stop. Do they have probable cause to stop me n after hundred similiar questions have me get out n start searching my car and going thru my phone. This good case for motion to suppress??? illegal search and seizure???

Avianna Moua @ 9/13/2016 6:25 AM

Why can an officer frisk clothing for weapons but not if the person is suspected to have drugs?

robert @ 11/28/2016 10:51 PM

I got into a non-violent shouting match argument with my exgirlfriend, My exgirlfriend is outside in the parking lot and I am inside my truck. Someone in the parking lot called the police, an officer comes to the scene and asked me to get out of my truck I have done no crime other than refusing to get out of my truck when the officer instructed at the time to get out of my truck and I get arrested and charged with pc 148 "resisting arrest" based on "reasonable suspicion" can someone please explain how this is possible? and how is "reasonable suspicion" is being used here?

Maegan @ 3/15/2017 11:38 PM

My boyfriend was on a bus and officers went on the bus and asked for his ticket, the ticket didn't have his name on it it was someone else's name. They asked if he had a bag and he said no. There was a bag under the bus matching the name on the ticket with drugs in it. Is that illegal search and seizure? And did they have probable cause to search the bag?

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