The Mysterium cosmographicum
and Kepler's Early Approach
to Natural Philosophy
IN 1621, looking back over an impressive career, Kepler commented that, “almost every book on astronomy which I have published since that time could be referred to one or another of the important chapters set out in this little book [the Mysterium cosmographicum], and would contain either an illustration or a completion of it” (MC, 39; KGW VIII, 9).1 Because Kepler viewed the Mysterium, his first book, as the genesis of his later astronomical works, I begin my discussion of the relationship between Kepler's philosophy and his new astronomy here. The Mysterium was written as an extended defense of Copernicus at a time when the empirical evidence did not favor the Copernican hypothesis over the Ptolemaic. Consequently, the defense had to be nonempirical, and Kepler based it on aesthetic, metaphysical, and methodological grounds.
To the modern reader the Mysterium might seem a strange book indeed, belonging only in a library of curiosities. But it is important to bear in mind that this book was well received at the time of its publication and popular enough to warrant a second edition. It even impressed Tycho Brahe, prompting him to invite Kepler to work for him.
The Mysterium is primarily about Kepler's notion of archetypes. Kepler believed that God created the world according to a plan. This plan, or pattern, is the archetype for the structure of the world (much like an architectural blueprint). Kepler believed, following the Pythagoreans and Plato, that this pattern was mathematical in nature and aesthetic in character. Because God created the physical world as a representation of this pattern, an archetypal model explains why the universe is the way it is. To use Aristotelian language (as Kepler often did), archetypal explanations provide an account of formal and final causes, rather than efficient or material causes (where an object's formal cause is its essential shape, its final cause is its purpose, and its efficient cause is the mechanism of its creation).2