 As we have displayed in  Table 2,  interpretations of mass-energy equivalence that hold that mass and energy are different properties disagree concerning whether there is some physical process by which mass is converted into energy (or vice versa). Although superficially Lange’s (2001, 2002) interpretation seems to fall in this category, as he certainly treats mass and energy as different properties, he differs from others in this category because Lange explicitly argues that only mass is a real property of physical systems. Consequently, we will discuss Lange’s interpretation separately below (in  Section 2.3.3).