In the law, causation is a description of the relationship between a given activity and the effect of that activity. People must prove causation when bringing suit in court to demonstrate that the defendant caused the outcome under dispute in court. This process involves showing that a person knew an action would have a predictable outcome and proceeded with the activity in awareness of this, exposing another party to the risk of harm.
Discussions of legal causation in court can become quite complex, and proving causation does not necessarily close a case, as there are situations where people can cause something, but not be liable. In a simple example, a person throwing a baseball while observing reasonable safety precautions would have no way to foresee a small child running onto the field and being injured. In this case, the injury would have been caused by the person throwing the baseball, but that person would not be held liable, as the consequence of the throw was not predictable.
In evaluations of causation, people look to see if the defendant engaged in a given action in a state of mind, indicating awareness of the consequences of that action. Someone who hurls a baseball at a house, for example, would be held liable for a broken window, for example, as a broken window is a reasonably foreseeable outcome if a projectile is thrown at a structure. One way to look at it is the so-called “but for” test, where people are asked to consider whether the harm would have happened if the defendant hadn't engaged in an activity.
Causation can follow a long and complicated chain, and in determinations of liability, people look not just as the immediate cause, but also the steps further back in the chain. Careful evaluation of the circumstances and the state of mind of the parties involved is needed when thinking about causation and developing a legal case. In the law, the ability of individuals to act under their own power in a variety of situations is considered when evaluating questions of liability.
Most legal systems have tests in place for helping people determine causation and argue their cases in court. These systems are based on legal scholarship, as well as some common sense, in terms of being able to evaluate activities and their predicted outcomes. In the pursuit of a case in court, people can question the parties involved, as well as witnesses, to see if people understood their actions and comprehended the potential impact of those actions.