There my own bad, and thus I never had

There are two types of mistake defenses to many American criminal prosecutions:  mistake of fact and mistake of law.1 


Mistakes of fact, in general, have a wider applicability as a successful defense to potential criminal prosecution for specific intent crimes than mistakes of law.  In a mistake of fact, the person or people who committed the allegedly criminal act misunderstood one or more related facts that negate an element of the alleged crime.2  For example, if I grab your black carryon bag off the luggage carousel at an airport and walk off with it, it may look like larceny.  However, if I had a similar black carryon bag checked in for the same flight, I may have a good defense to the alleged larceny: that I intended to get my own bad, and thus I never had any intent to deprive you of your property.  The mistake must be an honest mistake and reasonable.  Obviously, mistakes of fact don’t apply to strict liability crimes.3

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Mistakes of law are defenses to allegedly criminal behavior that assert that the perpetrator of the criminal acts did not know or understand the law concerning those acts.4  However, since it is a requirement for us to all know and understand the law, mistakes of law are rarely employed as a defense, and even more rarely are they successful.5  Mistakes of law can work as a defense in a few limited circumstances:


1)    When a new law has not yet been published.

2)    When the perpetrator cites a valid law or statute that was later changed

3)    When the perpetrator cites a valid judicial decision that is no longer applicable

4)    When the perpetrator states that he or she was advised of the validity of their acts by an appropriate official, perhaps a judge or a government official.6


Like in mistake of fact, the perpetrator’s reliance on a formerly valid law or statute, a formerly valid judicial decision, or incorrect advice of a judge or government official must be honest and reasonable.7


The Model Penal Code § 2.04(1) allows mistake of fact as a defense if it eliminates the mental state required for the allegedly criminal act.  Per the Model Penal Code, however, a defendant cannot cite mistake of fact as a defense if the defendant would still be guilty of another crime even if their mistaken belief had been correctly understood.8


Nota bene that mistake of fact, like voluntary intoxication, is not a defense to a criminal charge, per se.  Rather, mistake of fact can protect an alleged criminal from criminal prosecution in that mistake of fact can often eliminate the required mens rea, or intent, of committing a crime.



2. What does an ex post facto law do? What are the two major purposes of banning ex post facto laws? Give examples.




Ex post facto laws (“after the fact” in Latin) are ones that make conduct that was legal at the time, retroactively illegal.


Ex post facto laws are prohibited in state laws in the Constitution, Article I, Section 10, Clause 1: “No State shall enter into any Treaty, Alliance, or Confederation; grant Letters of Marque and Reprisal; coin Money; emit Bills of Credit; make any Thing but gold and silver Coin a Tender in Payment of Debts; pass any Bill of Attainder, ex post facto Law, or Law impairing the Obligation of Contracts, or grant any Title of Nobility.”9


Ex post facto laws prohibited








3. Define presumption of innocence. What is the importance of the presumption of innocence as it relates to criminal liability?



In the American criminal justice system, a person alleged to have committed potentially criminal acts is presumed innocent until proven guilty.10  This is the very foundation of our criminal law system.11  What this actually means is that we assume a defendant is innocent in the absence of contrary evidence Taylor v. Kentucky, 436 U.S. 478,  98 S. Ct. 1930, 56 L. Ed. 2d 468 1978).  The presumption of innocence is not considered evidence in favor of the defendant, nor must a judge or jury infer any particular conclusions regarding the defendant’s innocence nor from any particular piece of evidence. 


In the American criminal justice system, we must prove the elements of criminal acts and conduct beyond a reasonable doubt, as well.  This due process requirement was featured in the constitution (??) and in many statutes, judicial opinions, and in state laws of Alabama, Arizona, California, Delaware, Florida, Georgia, Kansas, Missouri, Montana, New York, North Carolina, Oklahoma, Texas, Vermont, and Virginia.12


In some cases, like in the Taylor v. Kentucky case cited above, the Court should issue jury instructions on the presumption of innocence, and in other cases, the Court should issue jury instructions on the need to prove guilty beyond a reasonable doubt.13


In many famous cases, the lack of issuing jury instructions on the presumption of innocence has been grounds for reversing a conviction on appeal, such as 1 2 3 4 5 6

The presumption of innocence is essential to the American criminal justice process.  The prosecution must prove the guilt of the defendant, for each count of alleged criminal activity, beyond any reasonable doubt.  A presumption of guilt, rather than innocence, is contrary to the principles of a democratic and free society with liberty.





4. List and explain the four elements of self-defense. Are there any exceptions to any of these elements? If so, explain. Use examples!



The defense of self-defense is a defense to certain criminal law charges (for example assault, manslaughter, or murder), as we are all allowed to use physical force to protect ourselves from injury, damages, or death.14

The four elements of self-defense are “(1) an unprovoked attack, (2) which threatens imminent injury or death, and (3) an objectively reasonable degree of force, used in response to (4) an objectively reasonable fear of injury or death.”15

Yes, there are exceptions to the elements.  For example, there are two exceptions to the unprovoked attack rule.  In one of those exceptions, if I am the defendant, and you punch me and then attack you with a knife, shoot a gun at you, and then fire my bazooka, it doesn’t matter that your attack on me was unprovoked, since my response to your unprovoked attack was not proportional to your attack on me.  My use of excessive force (and in this case, deadly force) in the retaliation renders the unprovoked attack element moot.  Deadly force is any force that could cause human death, such as my firing of my gun and bazooka.  Even if I don’t kill with the gunshot or bazooka shot, those were acts of deadly force because those shots could have killed someone.

Another exception to the unprovoked attack comes when one of the parties retreats or can retreat.  This is a complicated element of the law that is handled differently by different jurisdictions, but in general, even in an unprovoked attack on me, I have a common law duty to retreat if possible in most jurisdictions.16  Some jurisdictions have a stand-your-ground doctrine that allows me to use even deadly force to protect myself in an unprovoked attack.17

Another exception to an element to the defense of self-defense is the required element of imminent injury or death.  Case law has shown that battered wives can use force in self-defense even with no imminent threat of harm.18 


Self-defense can be a perfect defense to a crime, resulting in acquittal, or it can be imperfect,19 resulting in the conviction of a lesser crime and/or a lesser sentencing for that crime, such as when murder is dropped to manslaughter.  Self-defense can justify otherwise illegal conduct.20  Self-defense is a statutory defense in the majority of jurisdictions.


When deadly force is used in self-defense, some jurisdictions have extra requirements.  In fact, in some jurisdictions, when an initial attack is done without deadly force, the defendant cannot respond with deadly force.21  However, in other jurisdictions, a defendant can even protect property with deadly force.22


1 Tate, M. (2014). Criminal law and procedure: an overview. Thousand Oaks, CA: Sage Publications.

2 Samaha, J. (2015). Criminal law. St. Paul: West Publications.

3 Elies, V. S. (2012). Part 3 Defences, 10 Mistake of Fact and Law. Individual Criminal Responsibility in International Law. doi:10.1093/acprof:oso/9780199560363.003.0010

4 Dix, G. E. (2002). Criminal law. Chicago: Gilbert Law Summaries.

5 Samaha, J. (2015). Criminal law. St. Paul: West Publications.

6 Hall, L., & Seligman, S. J. (1941). Mistake of Law and Mens Rea. The University of Chicago Law Review, 8(4), 641. doi:10.2307/1597117

7 Samaha, J. (2015). Criminal law. St. Paul: West Publications.

8 Dubber, M. D. (2015). An introduction to the Model Penal Code. New York: Oxford University Press.

9 Stimson, F. J. (2012). Law of the federal and state constitutions of the united states.  Los Angeles: Hardpress Publishing, p. 115.

10 The Presumption Of Innocence In Criminal Cases, 3 Wash. & Lee L. Rev. 82 (1941),

11 Barton L. Ingraham, The Right of Silence, the Presumption of Innocence, the Burden of Proof, and a Modest Proposal: A Reply to O’Reilly, 86 J. Crim. L. & Criminology 559 (1996). Retrieved on December 25th, 2017 from

12 Second decennial edition of the American digest: a complete digest of all reported cases from 1906 to 1916. (1917). St. Paul: West Pub. Co.

13 The Presumption Of Innocence In Criminal Cases, 3 Wash. & Lee L. Rev. 82 (1941),

14 Samaha, J. (2015). Criminal law. St. Paul: West Publications.

15 Storm, L. M. (2015).  Criminal Law by Storm.  Morrisville, NC: Lulu Press, Inc., p. 166.

16 Alexander, L. (2016). Recipe for a Theory of Self-Defense. The Ethics of Self-Defense, 20-50. doi:10.1093/acprof:oso/9780190206086.003.0002

17 Guettabi, M., & Munasib, A. (2017). Stand Your Ground laws, homicides and gun deaths. Regional Studies, 1-11. doi:10.1080/00343404.2017.1371846

18 Ching, B. (2014). Mirandizing Terrorism Suspects? The Public Safety Exception, the Rescue Doctrine, and Implicit Analogies to Self-Defense, Defense of Others, and Battered Woman Syndrome. SSRN Electronic Journal. doi:10.2139/ssrn.2489725


19 Dix, G. E. (2002). Criminal law. Chicago: Gilbert Law Summaries.

20 Samaha, J. (2015). Criminal law. St. Paul: West Publications.

21 Supra.

22 The Use of Deadly Force in the Protection of Property under the Model Penal Code. (1959). Columbia Law Review, 59(8), 1212. doi:10.2307/1120032