We therefore cannot expect to treat these questions entirely separately. But we must start somewhere, and I will start by saying something about what causes and effects are. First, whatever they are, they must be entities of the same kinds, since most if not all causes are also effects. Suppose for example that a climber, Don, is killed by falling while climbing. The cause here, Don's falling, is also an effect, of whatever made him fall; and his dying, the effect, is also a cause, for example of grief in others. Thus finding out what causes are will also tell us what effects are.