Fleeting A in Genitive Plurals

What is Fleeting A in the Genitive Plural?
The genitive plural in Serbian typically ends in a long -ā (see генитив множине на -а). When a noun stem ends in a consonant cluster, standard Serbian resolves or accommodates this cluster using three primary strategies:
1. Inserting fleeting ā: An inserted vowel breaks the cluster before the regular ending -ā (e.g., девојка → девојака).
2. Taking the ending -ӣ: The cluster remains intact, but the noun takes the alternative ending -ӣ (especially frequent in feminine nouns, e.g., молба → молбӣ).
3. Direct attachment of regular -ā to unaltered clusters: Particularly typical for sibilant clusters (such as -ст, -зд, -шт, -жд), where neither vowel insertion nor ending change occurs (e.g., врста → врста̄, место → места̄).

In terms of accentuation, the inserted fleeting a is always long. It commonly carries a long rising accent (e.g., сеста́ра, ова́ца, зема́ља) or appears as a post-accentual length (such as пи̑са̄ма̄, which has a long falling accent on the initial syllable due to metatony before lengths). In disyllabic genitive plurals derived from monosyllabic oblique stems (such as пас / пса), the fleeting a receives a long falling accent: па̑са̄.

Which Nouns Take Fleeting A?

• Feminine nouns ending in -a: Many feminine stems ending in consonant clusters insert fleeting a:
  • девојка → девојака
  • сестра → сестара
  • овца → оваца
  • земља → земаља (note: љ functions as a single consonant)
• Neuter nouns ending in -o or -e: Stems ending in clusters frequently insert a:
  • писмо → писама
  • стакло → стакала
  • копље → копаља
  • крилце → крилаца
• Masculine nouns: Two main groups exhibit fleeting a:
  • Nouns that show непостојано а код именица in the nominative singular and take the short plural restore this fleeting vowel in the genitive plural: борац (G sg борца) → бораца; момак (G sg момка) → момака. Crucially, masculine nouns taking the expanded plural with the suffix -ови; -еви do not restore fleeting a; they attach the plural extension to the collapsed oblique stem: ветар (G sg ветра) → ветрови → ветрова; лакат (G sg лакта) → лактови → лактова; ручак (G sg ручка) → ручкови → ручкова.
  • Foreign loans and certain stems ending in consonant clusters (such as -нт, -кт, -пт, -рт, -кл) insert fleeting a specifically in the genitive plural: студент → студената, документ → докумената, аспект → аспеката, концерт → концерата, бицикл → бицикала.

Exceptions, Blockers, and Sound Changes:

• Cluster blockers (sibilant clusters): Stems ending in sibilant clusters like -ст, -шт, -жд, -шћ, as well as masculine stems ending in -ск and -зг, do not insert fleeting a. They retain their clusters unchanged: feminine врста → врста̄, башта → башта̄; neuter место → места̄, позориште → позоришта̄, ушће → ушћа̄; masculine диск → диска̄, киоск → киоска̄, мозак → мозгова̄.
• Alternative ending -и: Many feminine nouns never insert fleeting a and instead resolve the cluster by taking the ending -ӣ (e.g., молба → молбӣ, борба → борбӣ, лопта → лоптӣ, тајна → тајнӣ).
• Doublets: Some nouns permit both formations in standard Serbian (e.g., битка → битака / биткӣ; воћка → воћака / воћкӣ; приповетка → приповедака / приповеткӣ).
• Reversal of voice assimilation: When fleeting a intervenes between two consonants, it breaks their adjacency and reverses earlier voicing assimilation (једначење сугласника по звучности). For example, the underlying д in приповетка devoiced before к, but surfaces voiced once а separates them: приповедака.
• Interaction with L-to-O shift (прелазак Л у О): In masculine agent nouns ending in -лац (such as посетилац, гледалац, читалац), the л changes to о at the end of a syllable in oblique cases (G sg посетиоца, гледаоца). In the genitive plural, however, fleeting a steps between л and ц, keeping л in an open syllable and preventing the shift: G pl посетилаца, гледалаца, читалаца.