Ps.-Herodian’s treatise De barbarismo et soloecismo (Valckenaer/Villoison) cites theog. 321 ἦν τρεῖς ϰεϕαλαί as an example of the incorrect use of number as in this passage ἦν is accounted a third-person singular of εἶναι. This view is shared by several ancient and modern scholars, who regard the supposed incongruence as either a peculiarity of syntax or a figure (σχῆμα). In this paper I shall argue that there is morphological, dialectal, syntactical and stylistic evidence that theog. 321 ἦν is an original third-person plural of εἶναι. While discussing the plausibility of ἦν τρεῖς ϰεϕαλαί being a so-called σχῆμα Πινδαριϰόν I also suggest an old plural reading for Pind. fr. 78 Snell–Maehler.