Proto-Finnic/Phonology

Consonants
All consonants except, can be geminated. The geminated obstruents *cc, *kk, *pp, and *tt are subject to consonant gradation into half-long obstruents *c ' , *k ' , *p ' , and *t ' , respectively (see more at § Morphophonology). The voiced plosives are pronounced as fricatives when following vowels and, although the voiced plosives only fully merged with fricatives as suggested by assimilation into nasals in some languages ( →  → Finnish mm, nn, ng ). It is important to note that Estonian lacks phonemic, so the allophony are still preserved in some dialects.

Vowels
There are also phonemes, (written as ⟨ë⟩, ⟨ëë⟩  in Proto-Finnic contexts) in Southern Finnic, usually results from rounding of *e in back harmony words (*velka → *vëlka → Estonian *võlg), but also from other sporadic changes such as Southern Proto-Finnic *sëna : Northern Proto-Finnic *sana, SPF *hëbëda : NPF *hobeda, and SPF *mëistadak : NPF *muistadak. Because of this, some preferred to reconstruct words with *ë, at least dialectally (Southern Proto-Finnic).

Vowel harmony
Vowel harmony is a feature occuring in many Finnic languages, notable exceptions include (North) Estonian and Livonian. Proto-Finnic morphologically distinguished back vowels *a, *ë (in some dialects), *u, front vowels *ä, *e, *ö, *ü, and neutral vowels *i, *o. The vowel ö is always followed by front vowels, but o usually followed by back and neutral vowels, but can be preceded by all vowels.

Consonant gradation
Consonant gradation is a feature occuring in almost all Finnic languages, except Livonian, Ludic, and Veps. There are originally two types of consonant gradation: Radical gradation is restricted after vowels, sonorants (*l, *m, *n, *r), and homorganic stops, although it later extended to *h, *k albeit inconsistently. Gradated syllables also influenced preceding syllable's long vowel (*kee·li : *kee·len → *keeeli : *keelen → keel : keele "tongue") in Estonian.
 * Radical gradation: Occuring in non-initial closed syllables. This causes strong grade consonants become weak.

Note that *s → *h gradation is sporadic; and it largely occurs in s-stem nouns (nominative *pensas → genitive *pensahen "brush"), illative *-sen ~ *-hen, connegative past *-(t)tisen ~ *-(t)tihen. It also occured on the irregular noun *mees → genitive *meehen "man" (but maa → illative *maasen) All of the former examples are subject to suffixal gradation.

Suffixal gradation is restricted into intervocalic positions.
 * Suffixal gradation: Occuring in non-initial odd-numbered syllables. It is now less productive than radical gradation in modern languages, although it leaves some remnants such as the Finnish partitive suffix -ta changes -a after short vowels, otherwise -ta.