Jonatan Simons: eiusdem substantiae in Irenaeus: 4th century adaptation or 2nd century context?

Irenaeus speaks theologically of “same substance” and “different substance” five times in Against Heresies.Most of the occurrences are
only found in later Latin translations, and only the first occurrence (haer.1.11.3) is found in the Greek fragment of Epiphanius, allowing for a
(skeptical) reading that assumes that these texts were simply adjusted with a
Nicene slant (when ὁμοούσιος/eiusdem substantiae was recognized as essential). Another option, however, comes from the second century text Letter
to Florawhere “same/different” substance is the pinnacle of the argument.This paper will focus on the relevant passages in Irenaeus and compare them with the logic of Ptolemy to suggest that an argument, such as the one found in Letter to Flora,should be considered as a historical option for the presence of eiusdem substantiae in Against Heresies.Irenaeus
uses the concept once in summarizing Valentinian thought (haer.1.11.3), twice in discussing the nature of God in the generation of the Logos(haer.2.17.2, 2.17.7), once in relation to the nature(s) of Christ (haer.3.16.5),
and once in relation to the nature of covenants as they relate to Christ (haer.4.9.2). Because Valentinus is the one attributed with ὁμοούσιος, because
this concept is so central to the logic of Irenaeus’s argument for a simple God
and because there are other 2nd century texts with parallel arguments (namely, Letter to Flora), it seems advisable to consider the
concept of “same/different” substance as original to Irenaeus’s argument.