On page 89 of Peter and the Rock, Caragounis writes that "in normal [Greek] syntax a phrase like KAI EPI TAUTHi THi PETRAi can only refer to something outside of the speaker and his interlocutor. Therefore, if this phrase here--contrary to syntax--is to be referred to Peter, some very good reasons for this anomaly will need to be presented. However, to date no one seems to have been able to produce any such reasons. Consequently, it must be firmly asserted that Greek syntax goes against the assumption that PETRA refers to PETROS, and since there is no valid explanation for this violation of syntax, it must be concluded that there are no objective grounds for referring PETRA to PETROS."
He concludes (in this section of his book) that if Matthew had wanted us to think Peter is the "rock" of Matt. 16:18, he probably would have written: SU EI PETROS, KAI EPI SE OIKODOMHSW. This construction, avers Caragounis, "would have put the matter beyond reasonable doubt" (89).