A conceptual and methodological tension can be discerned among Enlightenment advocates of earth science, as regards extraterrestrial events and processes. True to the fundamental traditions of Theories of the Earth, many scientific thinkers exhibited clear recognition of the Earth's planetary status, as a member of a celestial family. To some this legitimated integration of a geological perspective into that of cosmology and astronomy. In extreme instances it even entailed an ideal of establishing earth science by deduction from principles of celestial mechanics. However, this integrative aspect of Theories of the Earth ran counter to another important element in the geological thinking of this era, one which asserted the overriding value of empirical investigation. In the minds of many empirical-minded champions of a natural history of the Earth, a true geology could only be built up through inductive discovery focussed exclusively on accessible terrestrial phenomena. Sometimes explicitly, often by merely tacit exclusion of extraterrestrial considerations, much geological investigation before 1800 tended to identify the integrity of the emerging science with the distinctively Earth-bound nature of the objects of study. The ideal of an autonomous geological science thus tended to be intertwined with a concept of terrestrial autonomy.
