  During the past one hundred years three related elementary particles - the
electron, the muon, and the tau - were discovered by very different scientific
techniques. The author, who received the Wolf Prize and the Nobel Prize for the
discovery of the tau, uses this history to discuss certainty and uncertainty in
the practice of science. While the emphasis is on the practice of scientific
research, the paper also explains for the non-physicist some basic ideas in
elementary particle science.
