gradáció
Gradáció, in linguistics, is the systematic alternation of sounds within a word to express different grammatical or semantic categories. It is a form of morphophonological alternation and can involve changes to vowels (ablaut or vowel gradation) or to consonants (consonant gradation). The phenomenon is cross-linguistically widespread and often tied to inflection or derivation, rather than to the addition of new affixes alone.
Vowel gradation occurs when the stem vowels change to signal tense, aspect, mood, or other grammatical distinctions.
Gradation serves several linguistic functions. It can encode grammatical information without increasing the number of morphemes,
Not all languages preserve gradation in the same way; in many languages it has become obscured or
See also: ablaut, morphophonology, consonant gradation, vowel harmony.