18. QVAEQVE RELICTA TIBI, SEXTE, VEL EMPTA TENES. The line seems rather prosaic. For the thought, compare Cic Off II 81 'multa hereditatibus, multa emptionibus, multa dotibus tenebantur sine iniuria'; for this sense of relicta, compare Nepos Att 13 2 'domum habuit ... ab auunculo hereditate relictam', Livy XXII 26 1 'pecunia a patre relicta', and Martial X xlvii 3 'res non parta labore, sed relicta'.
19. TAM TVVS EN EGO SVM. Professor A. Dalzell notes the play on the dual sense of tuus (devoted/belonging to you) which is probably the basis of the entire poem. For tuus 'devoted' compare Tr II 55-56 '[iuro ...] hunc animum fauisse tibi, uir maxime, meque, / qua sola potui, mente fuisse tuum' and the other passages cited at OLD tuus 6.
19. MVNERE. The word is difficult. 'Gift' seems strange in view of the stress placed on Pompeius' ownership of Ovid. Professor E. Fantham suggests to me that the phrase could mean 'by virtue of whose sad service you cannot say you own nothing in the Pontus', while Professor R. J. Tarrant suggests that munere could mean 'responsibility, charge', with cuius (=mei) as an objective genitive.
21. ATQVE VTINAM POSSIS, ET DETVR AMICIVS ARVVM. This elliptical use of posse seems to be colloquial. The only instance cited by OLD possum 2a from verse is Prop IV vii 74 'potuit [uar patuit], nec tibi auara fuit'; there as well the tone is that of lively speech.
21. AMICIVS ARVVM. The same phrase at Met XV 442-43 (Helenus to Aeneas) 'Pergama rapta feres, donec Troiaeque tibique / externum patrio contingat amicius aruum'. The use of the adjective amicus of things rather than person is in the main a poetic usage, but compare Cic Quinct 34 'breuitas postulatur, quae mihimet ipsi amicissima est', ND II 43 'fortunam, quae amica uarietati constantiam respuit', and Att XII xv 'nihil est mihi amicius solitudine'; other instances in the elder Pliny and Columella.
22. REMQVE TVAM PONAS IN MELIORE LOCO. Compare EP I iii 77-78 'liquit Agenorides Sidonia moenia Cadmus / poneret ut muros in meliore loco'.
24. NVMINA PERPETVA QVAE PIETATE COLIS. Tiberius and Germanicus are meant. For Pompeius' devotion to Germanicus, compare v 25-26 'tempus ab his uacuum Caesar Germanicus omne / auferet; a magnis hunc colit ille deis'.
25-26. ERRORIS NAM TV VIX EST DISCERNERE NOSTRI / SIS ARGVMENTVM MAIVS AN AVXILIVM. This distich does not belong in the text: it is in itself unintelligible, and interrupts a natural progression from 24 to 27. I am not certain that the distich is a simple interpolation, since there is nothing in the context to which it is an obvious gloss. Possibly it has been inserted from another letter from exile, in which its meaning would have been clear from context.
Argumentum is difficult. Wheeler translates, 'For 'tis hard to distinguish whether you are more the proof of my mistake or the relief', and notes 'Apparently Pompey could prove (argumentum) that "error" which Ovid regarded as the beginning of his woes'. But this seems a strange thing to say, for Ovid's error was hardly in need of demonstration.
Auxilium is used in its medical sense, erroris being equivalent to morbi or uulneris; compare RA 48 'uulneris auxilium' and the passages collected at OLD remedium 1.