Though scattered traces of athematic reduplicated presents can be found in several branches of Indo-European, it’s only Indo-Iranian and Greek that preserve them well enough to enable reconstruction. Indo-Iranian evidence is especially important, since that branch seems to distinguish two types reduplicated presents, one with *e and the other with *i as the echo vowel. Moreover, the ablaut (vowel alternations) in the conjugation of reduplicated presents can be seen there more clearly than in Greek.
- Vedic bábhasti, bápsati ‘chew, devour’, as if from *bʰe-bʰes-ti, *bʰe-bʰs-n̥ti ;
- Vedic jígāti, jígati ‘go’, as if from *gʷi-gʷah₂-ti, *gʷi-gʷh₂-n̥ti.
Some Indo-Europeanists believe that the two types are inherited and their coexistence in Indo-Aryan is an archaism rather than an innovation. In the LIV (p. 16)  they are reconstructed with different PIE vowel grades and accent patterns:
- Type 1: *dʰé-dʰoh₁-/*dʰé-dʰh₁- (root *dʰeh₁- ‘put, place’);
- Type 2: *sti-stéh₂- [*stistáh₂-]/*sti-sth₂- (root *steh₂- ‘stand’).
In Greek, on the other hand, the echo vowel is invariably *i, and the root vowel (when accented, as in the singular) is always a reflex of *e. Note the characteristic triad of examples (three very common verb roots, each with a different laryngeal):
- Greek títʰēmi ‘I put’, as if from *dʰi-dʰeh₁-mi;
- Greek hístēmi ‘I cause to stand’, as if from *s(t)i-steh₂-mi [*sistah₂mi];
- Greek dídōmi ‘I give’, as if from *di-deh₃-mi [*didoh₃mi].
|Type1 and Type 2|
It seems that Type 1 disappeared completely in the prehistory of Greek and all verbs originally belonging to it were absorbed by Type 2. The o-grade reconstructed in the LIV for Type 1 is not directly confirmed by Indo-Iranian evidence (all non-high vowels merged as /a/ there); it is inferred from rather complex assumptions about Proto-Indo-European vocalism. The only fact cited in its support is the anomalous o-grade present of Germanic *ðō- ‘do’ (found only in West Germanic). The idea that it represents dereduplicated *dʰé-dʰoh₁- inherited from Proto-Indo-European is hard to reconcile with our understanding of other reflexes of genuinely reduplicated *dʰeh₁- in Germanic (as we shall see).
Relics of reduplicated presents derived from *dʰeh₁- and *deh₃- [*doh₃-] can also be found in Balto-Slavic. The former had e-reduplication there, as shown by Lithuanian dẽda (3sg.) ‘lay, put’ and Old Church Slavonic deždǫ (1sg.) ‘put’ (< Proto-Slavic *de-d-je/o-, transferred to the *-je/o- conjugation). The latter, curiously, is reduplicated with Balto-Slavic *ō, as in Lith. dúodu, OCS damь (< *dad-mь < *dōd-mi, with athematic inflections). This *ō reflects earlier short *o, lengthened before non-aspirated *d (Winter’s Law). We can therefore reconstruct parallel reduplicated stems at an earlier stage of the Balto-Slavic parent language: *dʰe-dʰ- ‘put’, *do-d- ‘give’.
It’s clear that the “weak” form of the stem (with the root in zero-grade) was generalised in each case, but why are the echo vowels different? The most parsimionious explanation is that *dʰe-dʰ- is a straightforward reflex of PIE *dʰe-dʰeh₁-/*dʰe-dʰh₁- (levelled out in favour of the weak variant), whereas in the Balto-Slavic descendant of PIE *de-deh₃- [*dedoh₃-]/*de-dh₃- the echo vowel was assimilated to the laryngeally coloured root vowel of the “strong” stem (*dedoh₃- > *dodoh₃-). Subsequently, this new pronunciation was generalised across the paradigm (*dedh₃- > *dodh₃- > Proto-Balto-Slavic *dōd-), and only the weak variant survived into historical times. For this hypothesis to work, it is necessary to assume that the original strong vocalism of the reduplicated present of *dʰeh₁- was *e, not *o; otherwise it would also display the echo-vowel assimilation visible only in *dōd- ‘give’.
It seems reasonable to conclude that Type 1 and Type 2 differed much less than the LIV reconstruction suggests. The ablaut pattern of the root syllable seems to be the same in both types; the only significant difference between them concerns the choice of the echo vowel. This is how the two types are reconstructed e.g. by Don Ringe (2006: 28):
- Type 1: *dʰé-dʰeh₁-/*dʰé-dʰh₁-;
- Type 2: *stí-steh₂-/*stí-sth₂-.
Note the fixed accent on the echo syllable, consistent with most of the comparative evidence. On the other hand, this reconstruction doesn’t tell us why the root syllable alternates between e-grade and zero-grade. Nor does it help to account for the different echo vowels. Is the occurrence of e-reduplication beside i-reduplication just a messy fact of life, or are we missing something?
The two reconstructions can’t both be right, although they can both be wrong. I actually believe that neither of them is correct, and I’ll try to justify my opinion in the next post.
 The forms cited here are 3sg. and 3pl. The sequence *bʰs must have developed into something like Proto-Indo-Iranian *bzʰ as a result of progressive breathy-voice assimilation (Bartholomae’s Law). Although it ended up as voiceless [ps] in Vedic, the aspiration survived long enough to trigger the deaspiration of the initial consonant of bápsati by Grassmann’s Law.
 Helmut Rix, Martin Kümmel et al. 2001. Lexikon der indogermanischen Verben (2nd edition). Wiesbaden: Dr. Ludwig Reichert Verlag.