 In relation to the critically important concept of prediction, Popper makes a distinction between what he terms “conditional scientific predictions”, which have the form “If X takes place, then Y will take place”, and “unconditional scientific prophecies”, which have the form “Y will take place”. Contrary to popular belief, it is the former rather than the latter which are typical of the natural sciences, which means that typically prediction in natural science is conditional and limited in scope—it takes the form of hypothetical assertions stating that certain specified changes will come about if and only if particular specified events antecedently take place. This is not to deny that “unconditional scientific prophecies”, such as the prediction of eclipses, for example, do take place in science, and that the theoretical natural sciences make them possible. However, Popper argues that (a) these unconditional prophecies are not characteristic of the natural sciences, and (b) that the mechanism whereby they occur, in the very limited way in which they do, is not understood by the historicist.