But Tatian wrote within a comparatively short interval of Irenaeus.

It is sufficiently clear that Irenaeus held his opinion at the very time that Tatian wrote, though it was not published until later.

Here then we have a coincidence which makes it difficult to think that Tatian's four Gospels were different from ours.
The theory that finds favour with Credner [Endnote 241:3] and his followers, including the author of 'Supernatural Religion,' is that Tatian's Gospel was the same as that used by Justin.

I am myself not inclined to think this theory improbable; it would have been still less so, if Tatian had been the master and Justin the pupil [Endnote 241:4].

We have seen that the phenomena of Justin's evangelical quotations are as well met by the hypothesis that he made use of a Harmony as by any other.