With the overwhelming majority of crimes, defendants must act intentionally—or at least recklessly—in order to be guilty. Statutes that require intentional acts fall under the category of either "general intent" or "specific intent."
(For more on the mental state, or "mens rea," required to commit a crime, see How Defendants' Mental States Affect Their Responsibility for a Crime. Also see Can I be convicted of a crime if I didn't realize what I did was illegal?)
Most crimes require general intent, meaning that the prosecution must prove only that the accused meant to do an act prohibited by law. Whether the defendant intended the act's result is irrelevant.
Example: A state's law defines battery as "intentional and harmful physical contact with another person." This terminology makes battery a general intent crime. The intent element is satisfied if the defendant intends to cause harmful physical contact and actually causes it—it doesn't matter whether the defendant actually intended to hurt or seriously injure the victim. So, if Jill punches Jack in the eye after Jack calls her an "idiot," she has probably committed a battery. All the prosecution has to show is that Jill intentionally punched Jack. The prosecutor doesn't need to show that Jill intended to hurt Jack—the law assumes as much.
Specific intent crimes typically require that the defendant intentionally commit an act and intend to cause a particular result when committing that act. (U.S. v. Blair, 54 F.3d 639 (10th Cir. 1995).) In that regard, merely knowing that a result is likely isn't the same as specifically intending to bring it about. (Thornton v. State, 397 Md. 704 (2007).)
Example: A state's law defines aggravated battery as "intentional and harmful physical contact with another with the intent to maim or disfigure." This is a specific intent crime because it requires that the defendant not only cause harmful contact, but also with the purpose of maiming or disfiguring the victim. So, suppose that Denise says to Vance, "No one will love you once I mess up that pretty face." She then slices off his nose with a large, sharp razor blade. Since the evidence is likely to establish that she specifically intended to disfigure Vance, she is probably guilty of aggravated battery.
Example: A state's law provides that a person who takes another's property "with intent to deprive the owner is guilty of larceny." By describing the defendant's purpose in taking property, it is a specific intent crime. (Wetherelt v. State, 864 P.2d 449 (Wyo. 1993).)
Frequently, statutes don't clearly state whether the offenses they describe require specific or general intent. Rather, courts determine a crime's intent element by following the general rule that terms like "knowingly" and "voluntarily" denote general intent (as in "knowingly and voluntarily use force against another"). Terms that describe something more than knowledge and voluntariness, like "purpose," tend to indicate specific intent (as in "knowingly and voluntarily use force against someone with the intent to disable him or her"). (U.S. v. Peralta, 930 F. Supp. 1523 (S.D. Fla. 1996).)
Like so many areas of law, determining whether a crime requires general or specific intent can be tricky. If you've been charged with a crime, immediately consult an experienced criminal defense attorney. An experienced lawyer can fully explain the applicable law, advise you of any available defenses, and otherwise protect your rights.