 Many of the remaining "irregular" patterns of Finnish noun and verb inflection are explained by a change of a historical to .The change from to , a type of assibilation, is unconnected to consonant gradation, and dates back as early as Proto-Finnic.In modern Finnish the alternation is not productive, due to new cases of the sequence having been introduced by later sound changes and loanwords, and assibilation therefore occurs only in certain morphologically defined positions.