For a century, investigations of thunderstorms have been dominated by the idea that lightning is produced by a charge-separation process within the cloud caused by falling precipitation. The origin of this idea, its implications, present status, and probable future are examined in the light of T.S. Kuhn's views on the nature of scientific progress. Despite some achievements, the results of research based on the precipitation theory have proved disappointing. For example, they have shed little light on important problems such as the factors that determine the polarity of the cloud electric dipole and the role that electricity plays in meteorological processes. During this century, with the discovery of cosmic rays and the ionization they produce in the air above the cloud, it has become apparent that other processes, which do not involve contact charge separation or falling precipitation, are also causing electrification.
Thunderstorms exercise great influence, for both good and bad, on many human activities.
In view of their great environmental importance, it is surprising how little is known about them and how little effort is being made to understand how they work. It is urged that the present limited thunderstorm research activities be expanded to include new, and possibly more productive, approaches.