Strategic Approaches to the Legal Environment of Business. Michael O'Brien

if and only if conduct was necessary and sufficient to cause I alone. Written algebraically:

{ C }=A{ I }={ D }+{ O }	(Eqn. 1)
L≡{ N }−{ D }=ϕ and	(Eqn. 2)
L≡{ N }−{ O }≠ϕ	(Eqn. 3)

      Courts classically limited liability to Eqn. 2 articulating that actual cause was satisfied when “the harm would not have occurred absent the conduct.”35 However, the modern world is more complicated than that, and events often have many causes. Accordingly, courts look for whether the defendant’s conduct is a substantial cause of plaintiff’s harm.36 The difference in Eqn. 3 is that now, defendant’s conduct is actionable if it could have caused harm or it was sufficient to cause harm, but it is unknown whether that actually occurred.37 In Eqn. 2 cases, or “but for” causation, the plaintiff has the burden of proof to show that the act caused the harm. In Eqn. 3 cases that demonstrate necessary and sufficient condition causation, the burden shifts to the defendant to show that no factual cause existed.38 This distinction is shown in the Summers case below.

      Proximate cause is a limitation on the plaintiff’s ability to recover from the defendant. There are at least three theories on how proximate cause can be determined. The first is foreseeability. Where a judge determines that the event causing harm was highly extraordinary beyond the unpredictability of the defendant, then there is no foreseeability and no proximate cause.39