Motive. It is really big on TV shows. At the same time, if you listen to Wayne LaFave, it is completely irrelevant when it comes to substantive criminal law: The government is not required to prove motive in order to secure a conviction.
The New Oxford American dictionary defines “motive” as “a reason for doing something, esp. one that is hidden or not obvious.” This is much more helpful than a couple of other, more legalistic definitions that LaFave provides. For example, one such definition describes “motive” as “the desire coupled with the intention to bring about a certain consequence as an end, by means of other consequences which are also desired and intended but only as means.” (Don’t bother to read that back a second time – it still won’t mean anything.)
Describing that latter definition as “unsatisfying” (quite an understatement), LaFave provides the following example to illustrate the difference between “intent” and “motive.” If Person A murders Person B in order to obtain Person B’s money, Person A’s intention was to kill Person B. Person A’s motive was to obtain money.
LaFave then points out a couple of instances in which a person’s motive can in fact be relevant to criminal law. It might be relevant, for example, in cases of self-defense or necessity.
Finally, an offender’s reasons for engaging in proscribed conduct can often be relevant on the procedural side of criminal law:
For one thing, the existence of a good motive on the part of the guilty person may be taken into account wherever there is room for the exercise of discretion in the proceedings against that person. The police, taking into account the motives of the offender, may decide not to invoke the criminal process. The prosecutor, for the same reason, may decide not to charge the offender with a crime, or may charge him with a less serious offense than he actually committed. The jury, if the defendant’s good motive comes to its attention, might exercise its uncontrolled discretion to acquit. Motives are most relevant when the trial judge sets the defendant’s sentence, and it is not uncommon for a defendant to receive a minimum sentence because he was acting with good motives, or a rather high sentence because of his bad motives.