Tertullian Makes Clear that Justin and Irenaeus Wrote Two Different Works Against the Valentinians

My exposition will be limited to the original teachings of their chief teachers (= the Valentinians); it will not include the high-flying leaders of the mass of followers. I hope no one will say (because of this limitation) that I have invented this material for the occasion. No indeed, many men who were renowned for their holiness and their leadership, who were not only our predecessors but also contemporaries of those very her- esiarchs, have exposed and refuted them in learned volumes. I refer to Justin, philosopher and martyr, Miltiades, that churchly sage, Irenaeus, an eager discoverer of all doctrines, and our own Proculus, the living exemplar of a chaste old age and of Christian eloquence. In their footsteps I might hope to follow in all works of faith, just as I do in this work. Now if in reality there are no heresies at all (as you must believe if you assume those who refuted them invented them), the apostle who predicted them lied. But if in fact they do exist, they were none other than those which were examined by these men; no one can be considered to have enough leisure to invent material for his pen when he already has it at hand. (Against the Valentinians 5)

Clearly then this is a sign that Justin's work and Irenaeus's work (at least with respect to the Valentinians) were very different from one another.  This supports our contention that the Philosophumena's distinctiveness from Irenaeus's Against the Valentinians may be attributable to it deriving its origin from Justin's Syntagma.  I find it particularly intriguing that Valentinus knows of a tradition that the heresiarchs invented the heresies they wrote about (or at least misrepresented them).  This is also reflected to some degree in Hippolytus's report about the Marcites reaction to Irenaeus's report against them.