Planetary geomorphology: Some historical/analytical perspectives

•History provides examples of fixing beliefs (theories) in planetary geomorphology.•A priori presumptions and authority characterized the lunar cratering controversy.•Percival Lowell's Mars “canals” controversy illustrates the role of tenacity.•Controversy over the role of water on Mars has oscillated between extreme positions.

Three broad themes from the history of planetary geomorphology provide lessons in regard to the logic (valid reasoning processes) for the doing of that science. The long controversy over the origin of lunar craters, which was dominated for three centuries by the volcanic hypothesis, provides examples of reasoning on the basis of authority and a priori presumptions. Percival Lowell's controversy with geologists over the nature of linear markings on the surface of Mars illustrates the role of tenacity in regard to the beliefs of some individual scientists. Finally, modern controversies over the role of water in shaping the surface of Mars illustrate how the a priori method, i.e., belief produced according to reason, can seductively cloud the scientific openness to the importance of brute facts that deviate from a prevailing paradigm.