In this blog post, we examine from a philosophical perspective whether the necessary relationship between cause and effect can be applied identically at the group level.
People believe that every result always has a corresponding cause. The necessity of cause and effect can be generalized through individual cases. For example, if Person A became ill due to stress and Person B also became ill due to stress, the general causal relationship “stress is the cause of illness” is derived from these individual cases. Here, the causal relationship corresponding to individual cases is called ‘individual-level causation’, and the general causal relationship is called ‘group-level causation’. People have long believed that this group-level causation possesses necessity.
One reason people believe group-level causation is inevitable is that human thinking is primarily based on deductive logic. People synthesize individual cases gained through experience to derive general laws, and then use those laws to predict future events. For example, the law “When it rains, the road gets wet” was derived from observing that roads get wet in various situations where it rains. This deductive thinking tends to reinforce the perceived inevitability of causality. Consequently, causality derived at the group level gains a very high degree of credibility, serving as a crucial basis for people’s decision-making in daily life.
However, some argue that group-level causality should be understood as probable rather than inevitable. For instance, in the statement “stress is the cause of illness,” stress is not the necessary cause of illness but merely a factor that increases the probability of illness occurring. Even if A and B contract a specific illness, at the group level, one cannot assert that stress is the cause of that illness. Viewed this way, stress and illness are explained as being in a probable relationship, not a necessary one.
A crucial point in this debate is that the difference between necessity and probability is not merely one of degree. Necessity implies that a specific cause must lead to a specific effect, whereas probability means that a specific cause merely increases the likelihood of an effect occurring. Therefore, interpreting the statement “stress is the cause of illness” as necessary leads to the conclusion that everyone experiencing stress must become ill. Conversely, interpreting it probabilistically leads to the conclusion that stress increases the likelihood of illness but does not necessarily cause it.
Philosophers who argue that causation at the individual level and the collective level are independent believe these two levels of causation must be explained in different ways. This is because they consider the complexity and specificity inherent in individual-level causation to be inexplicable through collective-level causation. For example, Person A’s illness may stem from genetic factors, environmental factors, personal lifestyle habits, or arise through a process where these factors interact coincidentally and in complex ways. Considering this complexity, causation at the individual level may represent a necessity applicable only in specific cases, but when expanded to the group level, that necessity becomes diluted.
Those who argue that individual-level and group-level causation are connected maintain that even if multiple factors contribute to a disease, the necessity of causation still holds. If, when considering stress alongside all other factors in individual cases, stress remains an essential factor for the disease, then the necessity of individual-level causation is not undermined. Consequently, the necessity of group-level causation is also not undermined.
Ultimately, how we interpret causation at the individual and group levels profoundly alters our understanding of the relationship between cause and effect. This debate extends beyond mere philosophy, offering crucial implications for how we define and interpret causality in scientific research and social policy formulation. For example, when identifying the cause of a specific health problem and formulating policy based on this, an approach premised on necessary causation can lead to entirely different outcomes than one premised on probable causation. Therefore, this discussion transcends a mere philosophical debate and represents a critical issue with substantial implications for our lives.
