Theognostos 7 was the author of an extant work on orthography, published in J. A. Cramer, Anecdota Graeca, e codd. manuscriptis bibliothecae regiae parisiensis, (Oxford, 1839-1841) 2, pp. 1-165. See Hunger, Literatur II, pp. 19ff., ODB III, p. 2055. The work was dedicated to an emperor Leo; since he was alive in the 820s, the emperor was Leo V (Leo 15). Theognostos 7 also composed a description of the revolt of Euphemios 1 in Sicily (in 826/827), which was available to the author of the second book of Theophanes Continuatus (in the time of Constantine VII Porphyrogennitos): Theoph. Cont. II 27 (p. 82) (ἡ τότε γραφεῖσα Θεογνώστῳ τῷ περὶ ὀρθογραφίας γεγραφότι καὶ εἰς χεῖρας ἐλθοῦσα ἡμῶν).

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