The Finnish language, which belongs to the Finno-Ugric branch of the Uralic language family, has undergone several sound shifts throughout its history. These changes in pronunciation occurred as the language evolved from Proto-Finnic to Modern Finnish. Some of the most notable sound shifts include:

1. Loss of *x: The Proto-Finnic voiceless velar fricative *x was lost in Finnish, with no direct reflex.

2. Assimilation of *š: The voiceless postalveolar fricative *š was assimilated to *s in Finnish.

3. Loss of *δ: The voiced dental fricative *δ was lost in Finnish, with no direct reflex.

4. *o > uo, *ë > yö: The Proto-Finnic mid vowels *o and *ë shifted to the diphthongs uo and yö, respectively.

5. *ä > e: The Proto-Finnic front vowel *ä shifted to the Finnish front vowel e.

6. *ŋ > ŋk: The Proto-Finnic velar nasal *ŋ was replaced with the velar nasal followed by a voiceless velar stop (ŋk) in Finnish.

7. *ti > si: In Finnish, the voiceless alveolar stop *t was replaced with the voiceless alveolar fricative s when followed by the high front unrounded vowel i.

8. Consonant gradation: Finnish developed a system of consonant gradation, where the consonants in certain word forms alternate in a systematic manner, often affecting plosives and nasals. For example, the alternation between voiceless and voiced plosives (td, pb, k~g) and the weakening or deletion of certain consonants in certain forms (e.g., -kk- > -k-, -pp- > -p-, -tt- > -t-).

9. Vowel harmony: Finnish adopted a vowel harmony system, which dictates that certain vowels cannot appear in the same word as other specific vowels. The language is divided into three groups of vowels: front (ä, ö, y), neutral (e, i), and back (a, o, u). Front and back vowels generally do not appear together in the same native Finnish word.

These are some of the more significant sound shifts that have taken place as the Finnish language evolved from Proto-Finnic. It's important to note that linguistic evolution is complex, and this list is not exhaustive.
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