Causality

Causality is the relationship that exists between events when one event occurs as a consequence of the other. The first event is referred to as the “cause,” and the second event is known as the “effect.” There may be multiple causes and multiple effects; when this occurs, the causes are known as “factors” and the effects are known as “phenomena.” Causality sometimes proceeds in a chain of causes and effects, with one event causing one effect, which then causes another effect. Causality is one of the fundamental principles underlying philosophy, logic, theology, and science.

Background

The study of causality dates back at least as far as the Greek philosopher Aristotle (384–322 BCE). He is known for developing the theory of the four causes—material cause, formal cause, efficient cause, and final cause—though “explanation” is a more accurate term than “cause” for the concept he was describing. Aristotle was interested in causality because he was inquiring into the basic nature of and reason for existence, which required careful study of the surrounding world. A typical line of questioning might be as follows: “Why are we here?” “Because we were born.” “Why were we born?” “Because our parents conceived us.” In this way, Aristotle sought to move backward along the chain of causation to identify the “first cause” that had produced all subsequent events.

Overview

In the millennia since the time of Aristotle, ideas about causality have undergone many changes. The advent of Christianity and its spread throughout Europe interacted with the writings of Aristotle to convince many medieval and Renaissance thinkers that the first cause was God. God was sometimes known as the “prime mover” or “unmoving mover” because God was seen as the entity that existed before everything else, whose first action caused the rest of existence to come into being.

Later, with the arrival of the Enlightenment and its greater reliance on rational thought, philosophers such as David Hume (1711–76) expressed a more skeptical view of causality. By this time, many had begun to question whether human beings could ever truly perceive the nature of reality; some theorized that all of the information received from the senses—sight, smell, taste, touch, and hearing—might be nothing more than illusion. And if one could not believe one’s own eyes and ears, then how could a person determine that one event had produced another event? Perhaps the two events only seemed to be related when viewed from one perspective but would appear as random coincidences when seen from another. This kind of thinking gradually took hold and eventually evolved into more extreme forms, such as existentialism, which emphasizes the place of the individual and the exercise of their free will, and nihilism, which asserts that life is without inherent meaning and nothing is real in the way it is perceived to be.

Contemporary discussions of causality often refer to two different types of causation: necessary and sufficient. Necessary causation means that in order for a particular effect to be produced, the requisite cause must be present; however, the presence of that cause does not automatically mean that the effect will ensue. An example of this would be the two events of firing a gun and hitting a target a the bullet. Firing the gun is an event that is necessary in order for the bullet to hit the target, but the mere fact of firing the gun does not guarantee that the bullet will hit the target; the gun could be fired in another direction, or the person firing the gun could have poor aim. The second type of causation is known as “sufficient” because its presence does imply that the other event has occurred. An example of sufficient causality would be “If the bullet shot out of the gun, then the trigger was pulled.”

It is important to keep in mind that there is a distinction between conditions and causality. Conditions can be related to one another without a causal relationship being present. A causal relationship must have a temporal component—that is, one event must come before another in time. This is not the case with a conditional relationship. Because causal and conditional relationships are both frequently expressed using “if-then” statements, the two are often confused. An example of a conditional relationship is “If a stone is a diamond, then it is not a ruby.” Notably, there is no time relationship here; the stone does not fail to be a ruby after first being a diamond, nor is it a diamond after failing to be a ruby. What is being described is two mutually exclusive conditions, but no element of causality is present because not being a ruby does not cause a stone to be a diamond; it could just as plausibly be an emerald or a piece of granite.

Causality is of particular relevance to the field of statistical analysis. Most research attempts to determine causality in one form or another: Does a new drug cause patients’ levels of cholesterol to go down? Does a certain method of drilling for oil cause contamination of drinking water? As in the diamond-and-ruby example above, a common pitfall with this type of research is the confusion between causation and correlation; events may occur close to one another in time or may even be related to one another without there being a causal relationship between them. For example, a great deal of press coverage has been devoted to the suggestion that vaccinations administered to young children were the cause of some children later developing autism spectrum disorders. There have been a large number of studies that refute this claim, but because the origins of autism are poorly understood and the vaccines are administered not long before it becomes possible to diagnose a child with an autism spectrum disorder, many continue to believe that the vaccines must be the culprit.

Causality plays an important role in many areas of modern life. In courts of law, causation must be established in personal injury and negligence cases. For businesses, data scientists conduct research to better understand the causal link between marketing strategies, changes to products, and the introduction of new products, which helps guide business plans. Causality is also critical to the healthcare field.

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