This chapter suggests an analogy between the undetermined gender of the word comet and the undetermined nature of comets, which are neither planets nor stars nor both at the same time. In November 1664, a comet—the brightest since the three comets of 1618, say the reports of the time—appeared in the European skies. Jacques de Billy published two books on the 1664–1665 comets. Like Grandami's Parallèle des deux comètes, the short Traitè de la comète only attempts to establish that the first and the second are different comets, it ends with some brief considerations against judiciary astrology, against which Billy had already written a book. Like Billy, Pardies published two books on the 1664–1665 comets, one shorter in French and a longer one in Latin. Seventeenth-century France is often associated with Descartes's legacy, Descartes himself being often associated with a kind of speculative and anti-experimental philosophy.