Evidence of a habit (aka habit evidence), can be determinative in certain species of litigation.
The Federal Rules of Evidence (2010, United States), at §406:
"Evidence of the habit of a person or of the routine practice of an organization, whether corroborated or not and regardless of the presence of eyewitnesses, is relevant to prove that the conduct of the person or organization on a particular occasion was in conformity with the habit or routine practice."
In US ex rel. El-Amim, Justice Kollar-Kotelly adopted these words:
"A habit is a regular response to a specific situation. It refers to the type of nonvolitional activity that occurs with invariable regularity.
"A habit is considered to be probative because it is nonvolitional. It has a reflexive, almost instinctive quality. It is the semi-automatic character of the behavior which renders habit evidence trustworthy.
"Habit is a consistent method or manner of responding to a particular stimulus."
Or, similarly, this, from Justice Eckerstrom of the Arizona Court of Appeals:
"Habit evidence, as opposed to character evidence, is generally admissible. The rule contemplates conduct that is semi-automatic and regular.
"Habit describes one's regular response to a repeated specific situation, while character refers to a generalized description of one's disposition. Establishing habit requires more than a sparse selection of isolated episodes."1
- State v. Slover, 204 P. 3d 1088 at ¶16 (Court of Appeals of Arizona, 2009; note 1)
- US ex rel. El-Amin v. George Washington Univ., 533 F. Supp. 2d 12 (United States District Court, District of Columbia, 2008)