Much learning and ingenuity have been expended on this sentence, which, read as it stands in the text, appears to state that Marcion was an old man while Basilides and Valentinus were young men; and that Simon (Magus) was posterior to them in time. Marcion was certainly not an old man when Valentinus and Basilides were young men, as they flourished in the first half of the second century, and he was born about the beginning of it. The difficulty in regard to Simon is really best got over by supposing that Clement, speaking of these heresiarchs in ascending order, describes Marcion as further back in time; which sense μεθ’ ὅν of course will bear, although it does seem somewhat harsh, as “after” thus means “before.”