Commentary Par II 31-36

Dante's first impression of the physicality of the Moon tells us that its matter is less 'material' than earth's: For all its rock-like qualities, it seems a cloud.  As Singleton (DDP Singleton.Par.II.31) points out, Aristotle taught in De caelo that the Moon and all above is physically different from our material world.  It is thus that Dante must describe it as 'eternal,' since, unlike earth, it is imperishable.  That Beatrice, pure form, penetrates the matter of the Moon is not surprising; that Dante also does so raises the question in his mind that we find referred to in [Par II 37-39].