The most basic philosophical question in connection with risk is of course: What is risk? Unfortunately, this question is far from easy to answer, since the term “risk” has several well-established usages. Often, “risk” is used to denote, in general, a situation in which something unwelcome may or may not occur, but we do not know whether or not it will. This is how we use the term when we say, for instance, that smoking is a major health risk.
On other occasions, “risk” denotes the probability of an unwelcome event. This is how you use the word, for instance, if you ask a doctor how large the risk is that a treatment will fail. This is also the standard meaning of the term in decision theory; by “decision under risk” is meant “decision with determinate probabilities.”
A third usage is common in professional risk analysis. In that discipline, “risk” often denotes a numerical representation of severity that is obtained by multiplying the probability of an unwanted event with a measure of its disvalue (negative value). When, for instance, the risks associated with nuclear energy are compared in numerical terms to those of fossil fuels, “risk” is usually taken in this third, technical sense.
In all the different senses of “risk,” references to risk involve a subtle combination of knowledge and lack thereof. When there is a risk, there must be something that is unknown or has an unknown outcome. But, for this lack of knowledge to constitute ...