But-for test

The but-for test is a test commonly used in both tort law and criminal law to determine actual causation.  The test asks, "but for the existence of X, would Y have occurred?"  If the answer is yes, then factor X is an actual cause of result Y.

Of the numerous tests used to determine causation, the but-for test is considered to be one of the weaker ones. There are often two reasons cited for its weakness.

  1. Tenuous Relations Between Actions- 
    1. For example: Plaintiff was taking a different route to work than normal, because his normal route was closed for construction. The defendant steals the plaintiff's phone. But for the victim walking on the street that day, the crime would not have happened. Further, but for the city not closing the street that day, the crime would not have happened. So in this scenario, the defendant would actually shed some of his blame because of all of the other actions which led to the robbery, via but-for causation 
  2. Overcausation​
    1. The classic example of over-determination stems from an example which uses a firing squad. Under but-for causation, we cannot convict any of the members of the firing squad. We do not know whose bullet killed the victim, and  without having a specific defendant, the crime still happens. So because of this over-determination issue, we see a major issue related to but-for causation.

Some courts, however, have tried to solve the problems related to but-for cause. Some courts use the "Substantial factor" test, which states that as long as a defendant's actions were a substantial factor in the crime, then that defendant would be found guilty. So in the firing squad example, all of the members of the firing squad would be found guilty. However, this test creates a problem in which the members of the firing squad whose bullets did not harm the victim are still guilty, even though their actions did not lead to the victim's death. So courts have found four other ways to deal with the issues related to but-for causation.

  1. Likelihood of Survial Test
    1. This states that if the defendant's actions decreased the victim's chance of survival, then the defendant is guilty.
      1. Some courts (particularly in Nebraska), however, have rejected this test because they believe that the intervening action only presents a mere possibility that the person’s life would have been saved. As such, so we cannot be certain that the absence of that test actually contributed to the death (for example, under the likelihood of survival test, say that a doctor refuses to perform "x" surgery or test on the patient. After the doctor failed to perform the  surgery or test, the patient died. Under the likelihood of survival test, the doctor would be found guilty, because performing the test would have increased the likelihood of the patient's survival. However, courts that reject the test would say that the doctor's performance of the test or operation would not necessarily increase the likelihood of survival, because the patient may have still had the same change of dying, and so those courts would not find the doctor guilty). 
  2. Acceleration Theory
    1. This states that if the defendant's action caused a victim to die sooner than the victim would have otherwise died, then the defendant is guilty
      1. For example, If "X" fatally poisons "Y," but "Z" shoots and kills "Y," under acceleration theory, Z is convicted, rather than "X." Under normal but-for, Z would not have sole guilt for the death. Because of this problem, courts have not frequently applied this test.  
  3. Proximate Cause
    1. Some courts have scrapped but-for cause altogether, and simply apply the doctrine of proximate cause.
      1. This test asks whether the defendant's actions are closely enough related to the result to make the defendant responsible 
  4. Model Penal Code (MPC) Approach
    1. Some courts have scrapped both but-for and proximate cause, choosing instead to rely upon the MPC approach for causation, which finds the defendant liable if the result of the defendant's action involves the same kind of injury or harm as the probable result, and the result is not too remote or accidental in its occurrence that it actually has nothing to do with the defendant's liability or the gravity of his offense.