One skeptical view has arisen from the observation that theoretical definitions of life presume a theory of life (Cleland and Chyba 2002, Benner 2010, Cleland 2019). Although it is not obvious that the authors allude to the theory-theory of concepts, described in section 1, a common analogy is to early chemical theory. According to this analogy, early alchemists likened the alchemists’ Aqua regia (“royal water”) and Aqua fortis (“strong water”). Development of atomic theory revealed, Cleland argues, that the true nature of water was H2O, while the other ‘waters’ were  HNO3 + 3 HCl and HNO3, respectively. Cleland advocates avoiding definitions altogether, fearing they will blind us to new instances of life, and instead opts for tentative criteria, which she believes avoid the implicit dogma of even operational definitions.