Simple Athematic Present

Present: φημί, φῄ-ς, φη-σί, plural φᾰ-μέν, φᾰ-τέ, φασί

Imperfect: ἔ-φη-ν, ἔ-φη-ς and ἔ-φη-σθα, ἔ-φη, 1st plural φᾰ́μεν,[fn]For ἔ-φᾰμεν.[/fn] 3rd plural ἔ-φᾰ-σαν and ἔφαν, participle φάς

Middle: 2nd plural φά-σθε, imperfect ἐ-φᾰ́-μην, ἔ-φᾰ-το, imperative φά-ο, φά-σθω, infinitive φά-σθαι, participle
φᾰ́-μενος

And similarly

Present: εἶ-μι, εἶ-σθα, εἶ-σι, 3rd dual ἴ-τον, plural ἴ-μεν, ἴ-τε, ἴασι

Imperfect: 3rd dual ἴ-την, 3rd plural ἴσαν, imperative ἴ-θι, ἴ-τω, ἴ-τε

Infinitive: ἴ-μεναι (once ῑ), and ἰέναι

The 1st singular ἤϊα does not represent the original form of the imperfect, which would be ἦα (for ἠι̯α, Sanskrit âyam). Hence ἤϊα with the 3rd singular ἤει and 3rd plural ἤϊσαν, ᾖσαν must be formed like ᾔδεα and other pluperfects in -εα (§ 68.2); the ε of the original ἤεα, ἤεσαν being changed to ι under the influence of ἴ-μεν, etc., (Wackernagel, K. Z. xxv.266). For -σαν see § 40.

The forms ἤϊον (1st singular and 3rd plural), ἴεν, participle ἰών, are evidently produced by confusion with the thematic conjugation (§ 30, cp. also § 18).

The verb εἰμί I am is inflected as follows.

Imperative ἔσ-τω, ἔσ-τε, ἔσ-των; infinitive ἔμμεναι, ἔμεναι, ἔμεν, εἶναι; imperative middle ἔσ-σο (Od. 1.302).

The root ἐσ- is not reduced before heavy endings, as in the corresponding Sanskrit forms (dual s-vas, s-thas, s-tas; plural s-mas,
-tha,  s-anti; optative syâm), and the Latin sumus, sunt, sīm. The loss of σ in εἰμί, εἰμέν, ἦμεν (for ἐσ-μί, etc.) is according to Greek phonetic law: the Attic ἐσ-μέν is a new formation, due to the analogy of ἔσ-τι, ἐσ-τέ, etc. On the other hand ἦτε (Il. 16.557) follows ἦμεν; the older ἦσ-τε survives in Attic. The σ of ἦσαν belongs to the ending -σαν (§ 40), not to the root.

In the imperfect it is probable that we have an admixture of forms from the original perfect: thus ἦσ-θα (Sanskrit âsitha) is perfect, ἦα, for *ἦσα, is both perfect (Sanskrit âsa) and imperfect (Sanskrit âsam), ἦεν may be perfect (Sanskrit âsa) or thematic imperfect (answering to the Homeric 1st singular ἔον); the original 3rd singular imperfect survives in the Doric ἦς (Vedic âs). Again, the 2nd singular ἔησθα and 3rd singular ἔην, ἤην seem to require a stem (ἐ)ση-, found also in Latin e-rām (Brugmann, M.U. i. p.35), The -ν of the 3rd singular is unexplained: it does not appear to be the ν ἐφελκυστικόν, for we find no form *ἦε alongside of ἦεν.

Note that the 1st singular ἦν is not found in Homer.

The Homeric forms of εἰμί were discussed some years ago by L. Meyer (Κ. Ζ. ix. pp. 385, 423). He maintained that the Homeric 3rd singular imperfect was ἦεν or (without augment) ἔεν: the forms ἦν, ἔην and ἤην being due to corruption or misreading. The facts certainly give much countenance to this view, which has been adopted by Curtius (Stud. i. 2, 292) and Nauck. It can hardly be accidental that out of 54 places in which ἦν occurs in the thesis or second half of the foot, there are 50 in which it is followed by a vowel.

Il. 2.77 Νέστωρ ὅς ῥα Πύλοιο ἄναξ ἦν ἠμαθόεντος
Od. 17.208 ἀμφὶ δʼἄρʼ αἰγείρων ὑδατοτρεφέων ἦν ἄλσος

Moreover, out of 72 instances of ἔην there are 63 in which it is followed by a consonant (including ϝ). On the other hand, in 26 places ἦν occurs in the first half of the foot, and in 2 places it ends the line (in the phrase οὐδʼ ἄρα πως ἦν); and it is not easy to correct many of these so as to admit ἦεν or ἔεν. Again, ἦν and ἔην have some support in the 2nd singular forms ἦσθα, ἔησθα. (For ἔησθα Curtius proposed ἔεσθα, but there is no good reason for this.) And ἔην is found on an Ionic inscription of the 5th century (Röhl, no. 382). On the whole it seems that the argument for ἔεν is stronger than the argument against ἦν and ἔην. Perhaps we must recognize two stems, giving four forms: a stem ἐσ-, whence ἦεν, without augment ἔεν, and a stem (ἐ)ση- (Latin e-rām), whence ἔ-ην, without augment ἦν. The rare ἤην occurs followed by a vowel (so that we cannot read ἦεν) in 3 places only, viz. Od. 19.283 (al. εἴη, ἤειν), 23.316, 24.343. It may be due to mere "contamination" of ἦεν and ἔην. But no theory can be accepted as satisfactory that does not account for the fixed -ν of all these forms.

The α of ἔα is treated as long in 3 places, Il. 4.321, 5.887, Od. 14.352. In Od. 14.222 τοῖος ἔʼ ἐν πολέμῳ it is elided; but perhaps the ἐν may be omitted.

The vowel remains long before heavy endings in the stems

ἀη-, 3rd dual ἄη-τον, infinitive ἀή-μεναι, middle ἄη-το, participle ἀή-μενος
κιχη-, 3rd dual imperfect κιχή-την, 1st plural ἐ-κίχη-μεν, infinitive κιχή-μεναι, participle κιχή-μενος

except that it is shortened before -ντ and -ι (§ 6), as in the participle ἀέντες blowing, 3rd plural ἄεισι (for ἄε-ντι, in Hes. Th. 875), and the optative κιχε-ίη may find. The vowel is also long in ἔρῡ-το protected, infinitive ῥῦ-σθαι; and in all forms of κεῖμαι, ἧμαι, στεῦμαι.

A similar athematic inflection, in which the final vowel of the stem is long except before -ντ and -ι, appears in the Aeolic conjugation of verbs in -μι, as γέλαι-μι laugh, αἴνη-μι I praise (Hes. Op. 681), φίλη-μι love (1st plural φίλη-μεν, 3rd plural φίλεισι, participle φιλή-μενος), σάω-μι save. See § 19.