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Understanding Probable Cause

It's important to know what does and does not constitute PC for any given situation.

May 18, 2010  |  by Devallis Rutledge - Also by this author

Photo courtesy of Zuma Press.

Confusion. That's the best word to describe the state of understanding of the concept of "probable cause," which is often abbreviated as "PC." Not only is there widespread misunderstanding as to the meaning of the term, there's also a deeply entrenched practice among many law enforcement officers, lawyers, and judges of wrongly applying the probable-cause standard where it doesn't belong. Let's see if we can reduce the confusion.

"Probable Cause" Defined

The Fourth Amendment protects a right to be free from unreasonable searches and seizures, and it specifies that "no warrants shall issue, but upon probable cause." This makes it a constitutional requirement that search warrants and arrest warrants be based on probable cause. However, the Constitution does not define "probable cause" or give any examples of what does or does not constitute PC.

That task, as well as the job of figuring out when to apply the same standard to warrantless searches and seizures, was left for the courts to perform. Therefore, our body of law explaining and applying the concept is found in U.S. Supreme Court decisions, and sometimes in lower court decisions applying Supreme Court rulings.

Over the years, the Supreme Court has tried to describe the level of suspicion that would amount to PC, but it has always done so in general wording that leaves it up to courts to apply, case by case. In a 1949 opinion, the court said this about probable cause:

"The rule of probable cause is a practical, nontechnical conception. In dealing with probable cause, we deal with probabilities. These are not technical; they are the factual and practical considerations of everyday life on which reasonable and prudent men, not legal technicians, act. 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 man of reasonable caution in the belief that an offense has been or is being committed." (Brinegar v. U.S.)

The essence of this discussion is that it is not possible for judges and lawyers ("legal technicians") to assign some mathematical probability value for PC. Instead, the "technicians" must try to measure the facts of each case from a practical viewpoint and assess whether those facts would justify a reasonable officer in believing criminal activity was afoot.

Because some lower courts persisted in an effort to create a legal checklist of complicated "prongs" or "factors" to be evaluated, the Supreme Court made another effort to define PC in a 1983 case, saying the following:

"Perhaps the central teaching of our decisions bearing on the probable cause standard is that it is a practical, nontechnical conception. The process does not deal with hard certainties, but with probabilities. The evidence must be seen and weighed not in terms of library analysis by scholars, but as understood by those versed in the field of law enforcement. Probable cause is a fluid concept, turning on the assessment of probabilities in particular factual contexts-not readily, or even usefully, reduced to a neat set of legal rules." (Illinois v. Gates)

Translation: lower courts should stop using a law school approach to analyzing PC issues and simply consider how an officer in the field would understand the situation he or she confronted.

In a later decision, the court admitted that it had been unable to give a precise definition of probable cause but gave this guidance for lower courts engaged in assessments of probable-cause issues:

"The probable-cause standard is incapable of precise definition or quantification into percentages because it deals with probabilities and depends on the totality of the circumstances. The substance of all the definitions of probable cause is a reasonable ground for belief of guilt, and that the belief of guilt must be particularized with respect to the person to be searched or seized." (Maryland v. Pringle)

Translation: PC is a substantial suspicion, based on all the circumstances, that someone is a criminal.

"Probable Cause" Illustrated

Perhaps the best way to understand probable cause is by comparing it with other levels of suspicion or proof that are more easily understood.

PC is much less than proof "beyond a reasonable doubt," which is the much higher standard the prosecutor must meet in order to convict a defendant.

PC is much less than "clear and convincing" proof, which is the higher standard that must be met as to certain legal rulings, such as whether jury challenges were improperly based on group bias.

PC is less than a "preponderance of the evidence" (meaning 50 percent-plus), which is the plaintiff's burden of proof to win a civil case.

But PC is something more than the "reasonable suspicion" required to justify a temporary investigative detention.

Comments (14)

Displaying 1 - 14 of 14

aogden @ 7/25/2010 2:16 PM

I have a question. This was a great article, and really helped define the difference between PC, and reasonable suspicion. However, I was wondering whether or not the suspects permission plays into this at all. For example, if you engage a traffic stop, have the driver at your car, and ask if you can look through their purse or car.....if they say "yes", do you still need PC? Or, does the necessity of PC only come into play when they refuse to give consent?

In short, I guess i am asking this. On that traffic stop, you ask to search the car, and they say "no", IF you have PC, you can do it anyways. If you do not have legitimate PC, then you cannot, correct? But if they say "yes", you can search, even if you may not have enough to claim PC?

CognitiveConsistency @ 7/26/2010 8:34 PM


CognitiveConsistency @ 7/26/2010 8:38 PM


you only need consent in the absence of PC, or to widen the scope of your search. In the absence of PC, either consent to search or a warrant is needed.

aogden @ 7/29/2010 12:31 PM

Thank you! That makes sense. I hope to start the academy within the next 6 months in my local area here, so any insight I can get now, I will gladly take!!

SAM551974D @ 8/22/2010 11:06 PM

The author of this article's books which I have and I read on a regular basis are another tool needed to stay fine tuned and updated...a very good investment indeed! Reading the state's criminal codes and traffic codes are also a plus in my case all 1000 pages worth and most come with the CD for better call up's and refinement...of focus and search! With actual case examples break out the coffee pot...just keep the cup away from pages :-) Good Luck and stay safe!

shirley herbert @ 11/27/2011 10:14 AM

I was required to relinquish my 25 year old firearm because I registered it subsequent the expiration date of the amnesty period given for registering older firearms here in Illinois. I turned the firearm over to officers at my local police station and several police officers recommended that I purchase a Ruger 380 which is a purse size firearm. At the gunshop the seller also indicated to me that the Ruger is a purse size firearm for the purse (I live alone in a rough area in Chicago). Well, Illinois doesn't allow carrying of firearms concealed or not so. If I purchased the Ruger 380 and registed it in accordance with our ordinance, the police would have a record that I own the registered firearm. So, could probable cause (my having a registed purse size firearm that I may be carrying in my purse (which is breaking the law)) be applied by a police officer to search my purse when I am out and about?

leslie smith @ 3/16/2012 8:46 AM

If there is a sexual crime committed and there is an accused, can I seek a warrant from the court to get a DNA sample of another person who I believe is the actual person that did the crime?

e jones @ 6/16/2014 11:35 AM

stopped with no traffic offense commited the officer said he pulled me over because he knew i was driving on a suspended liscence... is this a legal stop????? e.jones

billwhip @ 12/7/2014 8:07 PM

to e jones: If the officer knows you and knows that you have a suspended license, and saw you driving, he has just observed a crime and can therefore stop you. You just gave him the PC to stop you by being in that car driving.

billwhip @ 12/7/2014 8:10 PM

@Shirley Herbert: If you cannot carry concealed in IL, having a gun in your purse is considered carrying concealed and therefore is illegal. If a cop saw you and knew you bought that gun and he knows you do not have a permit, that does not give him cause to stop you and search your purse. but if you commit a crime then yes he would most likely search your purse and if he finds your gun you would be added on another crime.

tim @ 5/17/2015 2:50 PM

@billwhip. simply committing a crime does not give PC for a search of a person. Knowles V Iowa specifically says you cannot search incident to citation. So say Shirley Herbert is trespassing. no other facts present than a simple trespass. Officers would not be able to search her purse and find that weapon without actually taking her to jail for the offense.

jacki @ 6/6/2015 3:05 AM

I was stopped after leaving a convenient store at 2 am with 3 friends. We were walking home with several bags of groceries and I had a shoulder bag I used to carry a few drinks. One officer frisked me then asked to search my bag, he took everything out, opened ever container, make up case, my sons in hailer even. He found a pill case and opened it finding a small empty bag. He said he wasn't going to charge me but I'd have to work the charge off by providing names. He gave me until 6pm that night to call or he'd file the paraphernalia charge. 3 days later I got charges in the mail. He filed them 6 hrs after the search at 8am.

concerned parent @ 12/9/2015 2:43 AM

My son was assaulted in school. When I came to see if he was ok, I was delayed by administrators to see my son. When I asked to see the Dean and or Resource officer I was told they were busy and I needed to make an oppointment. When I finally was able to see the Resource officer, I was shocked when he stated that upon questioning the assailant, he accused my son of robbing his weed that he was selling my son and questioned my son about the incedent without my presence even though I was there waiting. He was not arrested because my refusal to co operate with such an outlandish story coming from another student who assaulted my son. Now he has detained my son on probable cause. Is accusations by an admitted drug dealer credible? And is the Resource officer able to request detention of my son on probable cause? If the assailant is the only witness is he credible?

Advo99 @ 8/19/2016 2:48 PM

Reform - cops require more training, oversight.

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