Proximate cause is the initial act which sets off a natural and continuous sequence of events that produces injury. In the absence of the initial act which produces injury, no injury would have resulted. Any time you act, you start a series of natural and continuous events to occur (for example, after swinging your arm with a ball in your hand, you release it and the ball then rolls down a hill).

Responsibility for injury lies with the last negligent act that produces the injury (after the ball rolls down the hill, a stranger picks it up, throws it through a window which breaks the glass, causing the glass to shatter and strike a person who was sitting next to the window, cutting her arm and requiring her to obtain medical treatment). In this example, although you caused the ball to roll down the hill, your act is not the proximate cause of the injury to the lady sitting next to the window, the stranger's act is the proximate cause of the lady's injury and the stranger, not you, should be held responsible for the injury that she suffered.

Intervening Cause comes between one act (or failure to act) which alters the natural and continuous series of events that follows. When an intervening cause is present, since the natural chain of events have been changed due to the subsequent act of another, the initial actor may be relieved of the responsibility for an injury that is produced. In the example provided for proximate cause, the act of the stranger picking up the ball and throwing it through the window is an intervening cause which relieves you from the responsibility for injury which may have occurred as a result of your act. The responsibility for the injury to the lady is shifted and the stranger's act becomes the proximate cause for the lady's injury.