Although the matter is far from clear, what we call the cause rather than simply a causal factor or causally relevant factor seems to depend on a number of considerations. We tend to reserve the expression “the cause” for changes that occur prior to the effect, and describe permanent or standing features of the con- text as “causal factors” instead. That is how we speak about Legionnaires’ dis- ease. Being exposed to L. pneumophila, which was a specific event that occurred before the onset of the disease, caused it. Being in a run-down condition, which was a feature that patients possessed for some time before they contracted the disease, was not called the cause, but instead called a causal factor.
It is not clear, however, that we always draw the distinction between what we call the cause and what we call a causal factor based on whether something is a prior event or a standing condition. For example, if we are trying to explain why certain people who came in contact with L. pneu- mophila contracted the disease whereas others did not, then we might say that the former group contracted the disease because they were in a run- down condition. Thus, by limiting our investigation only to those who came in contact with L. pneumophila, our perspective has changed. We want to know why some within that group contracted the disease and others did not. Citing the run-down condition of those who contracted the disease as the cause now seems entirely natural. These examples suggest that we call something the cause when it plays a particularly important role relative to the purposes of our investigation. Usually this will be an event or change taking place against the background of fixed necessary conditions; sometimes it will not.