The first type of gradation affects geminate (long) plosives /pː, tː, kː/ (orthographically ⟨pp, tt, kk⟩), these are lenited to non-geminate versions /p, t, k/ in the weak grade.
By contrast, the stem pappi- and nominative plural suffix -t would form a word with two adjacent closed syllables (the ungrammatical *pappit *[pɑp.pit], with the geminate pp providing the onset of the second syllable), so the strong grade geminate pp appears instead in the weak grade: papit.
Originally, each voiceless stop altered to its voiced fricative equivalent (p to /β ~ v/, t to /ð/, and k to /ɣ/) but in contemporary Finnish, /ð/ is usually now pronounced as /d/, and /ɣ/ disappeared or changed.
Qualitative gradation can feed gliding, making the link between strong and weak forms more opaque.
[3] Some words, however, have truly exceptional qualitative gradation patterns that don't precisely fit into the general scheme explained above.
In some words where k might be expected to become j in the weak form, it isn't present altogether, such as in pyyhe : pyyhkeet 'towel(s)'.
These cases contrast with the typical pattern whereby k lenites to j when followed by e and preceded by h, as in pohje : pohkeet 'calf : calves' (on the leg).
In a subtype of qualitative gradation, the weak grade of a single plosive after a nasal or liquid becomes a copy of the preceding consonant.
Quantitative gradation is still productive in Finnish, i.e. it is applied to loanwords that enter the language (e.g. rokki : rokin "rock music").
By contrast, qualitative gradation applies only to words that were inherited from Proto-Finnic or the period shortly after it.
Speakers may attempt to inflect native words without gradation or other associated morphophonological alternations, if they are previously unfamiliar with the gradational inflection: e.g. paasi 'monolith' will often have the unalternating genitive singular paasin rather than alternating paaden (compare native vesi : veden 'water', versus recent loanword vaasi : vaasin 'vase').
The nominative plural suffix -t closes the final syllable, causing the weak grade to appear.
In the 1SG present and genitive singular, an extra e is inserted after the stem, which opens the syllable, hence creating a strong grade.
An example from the nominal domain is the inverse pattern pohjex : pohkeet, where superscript "x" represents the ghost consonant.
Ghost consonants are not pronounced between vowels, however, so resyllabification applies,[2] yielding /poh.kee-/ as the final version of the stem to which affixes are added.
The word tiedoton ("unknowing"), for example, features a weak grade d in the root, despite the fact that it is present in an open syllable.