In modern languages the prototypical accent is reflected in various ways, some preserving the Proto-Slavic situation to a greater degree than others.
The acute feature could occur independently of the accent, and Slavic retained this situation until at least the operation of Dybo's law.
Slavic also inherited from Proto-Balto-Slavic the distinction between fixed and mobile accentual paradigms in verbs and nominals.
The accent was then shifted back again in some forms by Ivšić's law, creating a new type of mobile pattern.
The most important difference between the two, in the context of the Slavic accent and prosody in general, is that the traditional viewpoint holds that Proto-Slavic retained all length distinctions as they were inherited from Proto-Balto-Slavic, whereas the Leiden school argues that some long vowels were shortened and short vowels were lengthened already in Proto-Slavic.
Within Balto-Slavic framework this matches with rising intonation of the cognate Latvian ⟨õ⟩ and length marks on the second part of diphthongs in Old Prussian.
[2] Some speculate that Proto-Slavic acute was phonetically in fact something entirely different, e.g. a glottalized syllable comparable to stød in Danish, or something similar.
[3][4] Perhaps, the most important difference from the "traditional" and "Leiden" schools is the use of morphophonological valences and the refusal of the Stang theory of the origin of the "new acute" in all forms as a result of accent retraction.
Phonetically reconstructed as an rising-falling syllable tone with a short, but sharp rising part and with a longer falling slope.
[17][18] Since Stang (1957) three accent paradigms (or accent types) are reconstructed for Proto-Slavic, traditionally marked with letters a, b and c. Their reflexes in individual Slavic languages are usually marked as A, B, C. Stang's original reconstruction was for nominals (nouns and adjectives), and Dybo (1963) subsequently expanded these to Proto-Slavic verbs as well.
Initial short/circumflex always "jumps" to the preceding syllable (a preposition or a conjunction) in a phonetic word; e.g. *nȃ rǭkǫ (Serbo-Croatian: nȁ rūku).
The Moscow accentological school, which reconstructs Proto-Indo-European and Proto-Balto-Slavic with underlying dominant and recessive syllables, posits four accent paradigms for Proto-Slavic rather than the standard three: a, b, c and d for nominals, and a, b1, c and b2 for verbs.
The suprasegmental vowel features of modern Slavic languages largely reflect the Proto-Slavic system, and are summarized in the table below.
[26] In many dialects the original Proto-Slavic accent position has changed its place; e.g. in literary Serbo-Croatian retracting by one syllable which yielded the new rising pitch (the so-called Neoshtokavian retraction), with old accent partly or fully preserved in nonstandard dialects (Old Shtokavian, Chakavian, Kajkavian).
Beside phonological causes, position of Proto-Slavic accent was often lost due to the leveling out within the mobile paradigm.
In the West Slavic languages it was accompanied by extensive contraction due to the loss of /j/, typically resulting in a long vowel.
The Proto-Slavic three-way opposition of old acute, short/circumflex and neoacute was in its original form lost in all Slavic languages.
If the final syllable is accented, then they sort of merge to form the traditional "rising" (instead of "low") and "falling" (instead of "high").
[29] About half of the dialects still retain the initial tonal differences, most of them being situated along the Sava river or in the northwest.
It also occurred in the volja-type nouns, where the exact explanation varies (according to the Leiden school, the final a was long).
[31] In monosyllables (whether due to loss of a yer or original), the rightward shift was blocked and the falling accent was lengthened without movement.
It also occurred in northern Styrian dialect plane, however not fully as the antepenultimate syllables still stayed short.
The newly accented syllable was initially short, but now only Tolmin, Cerkno, part of Rosen Valley, part of Jaun Valley, Prlekija and Premurje dialects still have not lengthened them, while in some (e. g. Upper Carniolan dialect) it even became falling (while still retaining pitch distinctions).
The newly accented syllable mostly stayed short; the exception are dialects which eliminated length distinctions or some less common cases where it vocalised into /a/ and then lengthened.
Distribution of rising and falling vowels also varies drastically between dialects and current standard contains a lot of metatony, mostly from acute to circumflex.
A vestige of the former pitch accent remains in the outcome of the liquid diphthongs *el, *er, *ol and *or, which undergo so-called pleophony (полногла́сие polnoglásiye).
This moves the stress to the last syllable of the stem in particular areas: plural cases in nouns, the long form in adjectives, the present tense other than the first person singular in derived verbs, and the infinitive and past forms in non-derived verbs (this last actually deriving from Hirt's law).
Beside the contrastive tone (rising vs. falling), the Late Proto-Slavic also had a vowel quantity (long vs. short) which was phonemically non-distinctive.
In other words, long vowels could occur in:[35] Old East Slavic and Old Polish loanwords in Finnish, Karelian, Estonian, Lithuanian and Latvian show that the length of the originally long vowels in Slavic (*a, *ě, *i, *u, *ǫ, *ę) is retained regardless of the intonation, the position in the word or the number of syllables.
[37] After surveying the data with respect to stress type (acute, short/circumflex, neoacute), the number of the syllables in a word, the position (stressed, pretonic or posttonic) and the accentual paradigm (a, b or c), Kapović (2005) offers the following reflexes for West Slavic, and Serbo-Croatian, which have retained distinctive lengths: