这份概览包括语言学家对印欧语系中的各种语言总结出的音变规律。每个规则都给出了简洁的描述；在各自的主页面中提供了更多详细信息。

In all words or word-groups of four or more syllables bearing the chief accent on a long syllable, a short unaccented medial vowel was necessarily syncopated, but might be restored by analogy