 In this section, we will describe the merits and demerits of each of the interpretations in  Table 2.  Beyond these interpretations, we will also discuss two other types of interpretations of mass-energy equivalence that do not fit neatly in  Table 2.  First, we will discuss Lange’s (2001, 2002) interpretation, which holds that only mass is a real property of physical systems and that we convert mass into energy when we shift the level at which we analyze physical systems. Second, we will discuss two interpretations (one by Einstein and Infeld, 1938 and the other by Zahar, 1989), which we will call ontological interpretations, that attempt to answer question (3) above affirmatively. However, we begin this section by addressing what has formerly been a fairly common misconception concerning mass-energy equivalence.