In his book Περὶ τῆς τοῦ λόγου συντάξεως Michael Syncellus includes a section on the rules for accenting prepositions that occur in anastrophe (1128–204, §§ 144–9). This section is also part of the chapter on the accentuation of prepositions preserved in the Τονικὰ παραγγέλματα by John of Alexandria (26.13–28.19), an important epitome of Aelius Herodian's lost work Περὶ καθολικῆς προσῳδίας. Further below (1595–606, § 189, and 1614–43, §§ 191–2), Michael's treatment of the various functions of the conjunction ἤ/ἦ (διαζευκτικός, παραδιαζευκτικός, διασαφητικός, διαπορητικός, διαβεβαιωτικός) again presents very strong similarities with the corresponding unit of the chapter on the accentuation of conjunctions in the Τονικὰ παραγγέλματα (41.1–42.24). In this article I first argue that Michael's sections, which have gone entirely unnoticed by students of the Cath. Pr., have drawn directly upon the Cath. Pr., and I identify the ways in which they add to our picture of Herodian's and John's aforementioned works. Then I turn my attention to John's chapter on the accentuation of prepositions: I provide additional evidence to support Eduard Hiller's view that it does not form a coherent whole, and I discuss the implications of this problematical structure for defining the contents of Book 18 and the Appendix of the Cath. Pr.