According to Field, it is impossible to decide which of these two affirmations is true. Prior to the theory of relativity, the term "mass" was "referentially indeterminate". But this does not mean that the term "mass" did not have a different "meaning" than it now has. The problem is not one of meaning but of "reference". The reference of such terms as mass is only "partially determined": we don't really know how Newton intended his use of this term to be applied. As a consequence, neither of the two terms fully denotes (refers). It follows that it is improper to maintain that a term has changed its reference during a scientific revolution; it is more appropriate to describe terms such as "mass" as "having undergone a denotional refinement."