The proto-Finnic language underwent several sound shifts over time, which contributed to the development of the modern Finnish language. 

Some of the most significant sound shifts include:

1. The loss of the Finno-Ugric initial consonant cluster *pl- and *pr-.
2. The development of vowel harmony through the assimilation of vowels based on the back or front position of the first vowel in the word.
3. The development of the Finnish consonant gradation system which involves the alternation of consonants between weak and strong forms.
4. The disappearance of certain vowel combinations such as diphthongs in words.
5. The palatalization of certain consonants before front vowels.

These sound shifts are essential to understanding the development of the Finnish language over time.
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