This paper provides an overview of recent historical research regarding scientifically-informed challenges to the idea that the stars are other suns orbited by other inhabited earths – an idea that came to be known as ‘the Plurality of Worlds’. Johannes Kepler in the 17th century, Jacques Cassini in the 18th and William Whewell in the 19th each argued against ‘pluralism’ based on what in their respective times was solid science. Nevertheless, pluralism remained popular despite these and other scientific challenges. This history will be of interest to the astronomical community so that it is better positioned to avoid difficulties should the historical trajectory of pluralism continue, especially as it persists in the popular imagination.

Kant was not the first in whom the ‘starry heavens’ above us inspired awe and wonder. For Kant, who was firmly convinced of the existence of inhabitants of other worlds, these heavens were inhabited. He is certain that ‘If it were possible to settle by any sort of experience whether there are inhabitants of at least some of the planets that we see, I might well bet everything that I have on it. Hence I say that it is not merely an opinion but a strong belief (on the correctness of which I would wager many advantages in life) that there are also inhabitants of other worlds.’ In this statement by Kant in no less a work than the Critique of Pure Reason one can, on the one hand, recognize a reflection of Kant's earlier convictions and expositions, on the other hand, the context of the citation and the contemporary background are, of course, relevant. Following the example of Kant, this paper investigates the meaning of such reflections about inhabitants of alien worlds, which due to advances in planetary astronomy are today again on the agenda. Consideration of this subject also represents a challenge for theology.