Causation is the "causal relationship between the defendant's conduct and end result". In other words, causation provides a means of connecting conduct with a resulting effect, typically an injury. In criminal law, it is defined as the actus reus (an action) from which the specific injury or other effect arose and is combined with mens rea (a state of mind) to comprise the elements of guilt. Causation only applies where a result has been achieved and therefore is immaterial with regard to inchoate offenses.

Background concepts.

Legal systems more or less try to uphold the notions of fairness and justice. If a state is going to penalize a person or require that person pay compensation to another for losses incurred, liability is imposed according to the idea that those who injure others should take responsibility for their actions. Although some parts of any legal system will have qualities of strict liability, in which the mens rea is immaterial to the result and subsequent liability of the actor, most look to establish liability by showing that the defendant was the cause of the particular injury or loss.

Even the youngest children quickly learn that, with varying degrees of probability, consequences flow from physical acts and omissions. The more predictable the outcome, the greater the likelihood that the actor caused the injury or loss intentionally. There are many ways in which the law might capture this simple rule of practical experience: that there is a natural flow to events, that a reasonable man in the same situation would have foreseen this consequence as likely to occur, that the loss flowed naturally from the breach of contractual duties or tortuous actions, etc. However it is phrased, the essence of the degree of fault attributed will lie in the fact that reasonable people try to avoid injuring others, so if harm was foreseeable, there should be liability to the extent that the extent of the harm actually resulting was foreseeable.