Do Causes Necessitate Their Effects?
This issue we have confronted many times before, in considering the cosmological argument
from Plato through Aquinas. I have labelled this issue "modality". Some, including al-Farabi and
ibn Sina, have clearly endorsed the thesis that causes necessitate their effects. This thesis also
seems to be implicit in the principle of sufficient reason. If a cause does not necessitate its effect,
then it does not provide a truly suficient reason for it, since we could still ask why, in this case,
the cause was followed by its effect.
Nonetheless, I will argue that causes do not typically necessitate their effects. In fact, I am
inclined to think that they never do. There are four reasons for this conviction. First, if causes
necessitate their effects, and effects likewise necessitate their causes, then we no longer have an
account of the asymmetry of causation. In addition, it is difficult to see how we could maintain
the idea that causes and effects are separate existences, if they mutually imply each other.
Second, if we supposed that causes necessitated their effects, then we would be led to an
inflation of causes. For example, suppose there is an explosion in Welch hall that is caused by the
presence of flammable gas, oxygen and a spark. These three conditions do not necessitate the
explosion: in addition, there are infinitely many negative conditions that must be specified. For
example, the explosion would not have happened had there been fire extinguisher foam in the
lab. Similarly, if the hall had been full of water, the explosion would have been prevented. If
causes necessitate their effects, then the cause of the explosion must include the absence of fire
extinguishing foam, the absence of water, and the absence of infinitely many other conditions.
This point does not depend on rejecting determinism. Even if the world were deterministic, so
that there was a sufficient condition for every event, we could still say that causes do not
necessitate their effects. We could include only the positive facts within the cause, omitting all of
the mererly negative conditions that would have to be added to construct a sufficient condition.
Third, there are a number of thought experiments that suggest that causation is possible without