Sievers's law in Indo-European linguistics accounts for the pronunciation of a consonant cluster with a glide (*w or *y) before a vowel as it was affected by the phonetics of the preceding syllable.
Thus in the Rigveda dāivya- "divine" actually had three syllables in scansion (dāiviya-) but satya- "true" was scanned as written.
[citation needed] For example, the Sanskrit "tool-suffix" -tra- (e.g. pā-tra- "drinking cup, vessel") almost always follows a consonant or long vowel and should have therefore been -tira-; but no such form as **pōtira-, either written as such or scanned thus, is actually attested in the Rigveda or any other Indic text.
Edgerton also maintained that the phonotactic rules in question applied to sequences arising across morpheme boundaries, such as when the bahuvrīhi prefix *su- occurred before a noun beginning with *w- (e.g. *su-wiHro- "well-heroed", Vedic suvīra-).
He cited several hundred passages from the Rigveda, which he claimed should be rescanned to reveal hitherto unnoticed expressions of the syllable structure called for by his theory.
But most forms show no such direct expressions; for them, Edgerton noted sharply skewed distributions that he interpreted as evidence for a lost alternation between syllabic and nonsyllabic consonants (commonly called "semivowels" in the literature).
Thus say śiras "head" (from *śr̥ros) has no monosyllabic partner **śras (from **śros), but Edgerton noted that śiras occurred 100% of the time in the environments where his theory called for the syllabification of the *r. Appealing to the "formulaic" nature of oral poetry, especially in tricky and demanding literary forms like sacred Vedic versification, he reasoned that this was direct evidence for the previous existence of an alternant *śras, on the assumption that when (for whatever reason) this *śras and other forms like it came to be shunned, the typical collocations in which they would have (correctly) occurred inevitably became obsolete at the same time as the loss of the form itself.
Parenthetically, many of Edgerton's data on this point are inappropriate: current scholarship takes śiras, for example, to be the regular reflex of PIE *ḱr̥Hos, the syllabicity of the resonant resulting from the fact that it was followed by a consonant in Proto-Indo-European; there never was, nor could have been, a form **ḱros to yield Indic **śras.
And indeed such skewing in distribution is pervasive in Vedic vocabulary: śatam "100", and dozens of other forms with no bearing on Edgerton's law, have exactly the same strong preference for not following a word ending with a short vowel that e.g. śiras "head" does, presumably by reason of beginning with a single consonant followed by a light syllable.
A second difficulty has emerged much more recently (Sihler 2006): The actual passages from the Rigveda cited in Edgerton's two large articles in 1934 and 1943 as examples of the effects of his theory in action seriously misrepresent the facts in all but a handful of cases.
No more than three Rigvedic passages cited in the 1934 article, and none at all in 1943, actually support the claims of Edgerton's law regarding word-initial sequences.
And it has been shown also that the apparent success of Lindeman's more modest claims are not without troubling problems, too, such as the limitation of the reliable examples to semivowels (the glides *y and *w) even though such alternations in the other four consonants should have left robust outcomes (for example, a disyllabic form of prá "forth, away" should have been very much more frequent than the monosyllable, which would have occurred only after a word ending in a short vowel; but there is no evidence for such a disyllabic form as **pirá, in Vedic or any other form of Indic); and that the syllabified alternants (e.g. *diyēws) are very much rarer than they should be: they account for only fifteen to twenty percent of the total: they should account for at least eighty percent, since the monosyllabic form would have originally occurred, like prá, only after a word ending in a short vowel.
In addition to the Gothic nouns cited above, Gothic strong adjectives show a light suffix -ji- following a light stem, yielding the nominative singular masculine midjis "middle", while a heavy suffix -ī- (from -iji-/-ija-) follows a long stem: wilþeis /wilþīs/ "wild".
In the oldest attested languages, medial syllabic -ij- tends to be lost in the same way as in Old Norse, while nonsyllabic -j- (occurring only after -r-, which was not geminated) is preserved.
Donald Ringe, in his book "From Proto-Indo-European to Proto-Germanic", characterizes the origins of the different features as follows: Sievers's law in Germanic was clearly conditioned on morphological grounds as well as phonological, since suffixes were treated as separate words if they were recognised as separate morphological segments.