Changes:

• Singular forms: -nen turns into -se-
• In the singular partitive, the -nen will be replaced with -stA. (More theoretically, you will use the consonant stem of the word (e.g. nais-) and add -tA to it).
• Plural forms: -nen turns into -si-
• In the plural genitive, the -nen can be replaced with -sten (consonant stem) or -sien (vowel stem).

Separate articles:

• Nouns ending in -nen
• Common adjectives ending in -nen
• Loanwords ending in -nen
• Words ending in -inen
• Words ending in -llinen

• Old words ending in -is will have -is- turned into -ii-.
  
• This -ii- is present in both the singular and the plural case, which makes them look identical.
• The singular partitive’s -tA is added to the basic form of the word.

• Singular forms: -is becomes -ikse-
• Singular partitive: basic form plus -tA
• Plural forms: -is becomes -iksi-
• The plural genitive can either be made from the consonant stem (e.g. roskisten) or from the vowel stem (e.g. roskiksien).

• Comparison of -is-ii- and -is-ikse- nouns
• Spoken language words ending in -is

• Singular’s weak forms: -Us turn into -Ude-
• Mihin and essive forms: -Us turns into -Ute-
• Singular partitive: -s turns into -ttA
• Plural forms (except for the T-plural): -Uksi-

• Singular forms: -Us turns into -Ukse-
• Singular partitive: basic form plus -tA
• All plural forms: -Us turns into -Uksi-
• The plural genitive form can be both made with the vowel stem (e.g. tarjouksien) and the consonant stem (e.g. tarjousten).

• Comparison of -us-ude- and -us-ukse- nouns
• Words -US/-YS → -UDE-
• Words -US/-YS → -UKSE-

• Singular forms: -Os turns into -Okse-
• Singular partitive: basic form plus -tA
• Plural forms: -Os turns into -Oksi-
• The plural genitive can have both a vowel stem (e.g. ostoksien) and a consonant stem (e.g. ostosten).

• Words ending in -Os

• Words ending in -As belong to wordtype B.
• Singular forms: -As turns into -AA-
• Singular partitive: basic form plus -tA
• Plural forms: -AA turns into -Ai-
• The plural genitive can end in both -den (e.g. lampaiden) and -tten (e.g. lampaitten).

• This is a really rare occurrence for only a couple of words.
• Singular forms: -As turns into -Akse-
• Singular partitive: basic form plus -tA
• Plural forms: -As turns into -Aksi-
• The plural genitive can both have a vowel stem (e.g. lihaksien) and a vowel stem (e.g. lihasten).

• Words ending in -As

• Words ending in -in belong to wordtype B.
• Singular forms: -in turns into -ime-
• Singular partitive: basic form plus -tA
• Plural forms: -in turns into -imi-
• The plural genitive can have a vowel stem (e.g. soittimien) or a consonant stem (e.g. soitinten).

• Words ending in -in

• Singular forms: -nut/nyt turns into -nee-
• Singular partitive: basic form plus -tA
• Plural forms: -nut/nyt turns into -nei-
• The plural genitive can end in both -neiden (väsyneiden) and -neitten (väsyneitten).

• Words ending in -nut/nyt

• Words ending in -tAr belong to wordtype B.
• Singular forms: -tAr turns into -ttAre-
• Singular partitive: basic form plus -tA
• Plural forms: -tAr turns into -ttAri-
• The plural genitive can both have a vowel stem (e.g. tyttärien) and a vowel stem (e.g. tytärten).

• Words ending in -TAR → -TTARE-

• Words ending in -tOn belong to wordtype B.
• Singular forms: -tOn turns into -ttOmA-
• Singular partitive: basic form plus -tA
• Plural forms: -tOn turns into -ttOmi-
• The plural genitive can both have a vowel stem (e.g. työttömien) and a (much rarer) vowel stem (e.g. työtönten).

• Words ending in -TON → -TTOMA-

• Singular forms: -es turns into -ekse-
• Plural forms: -es turns into -eksi-
• Singular partitive: basic form plus -tA
• Plural genitive: can have either a vowel stem (e.g. juureksien) or consonant stem (e.g. juuresten).

• Singular forms: basic form plus -e-
• Plural forms: basic form plus -i-
• Singular partitive: basic form plus -tA
• The plural genitive can have either a vowel stem (e.g. jäsenien) or consonant stem (e.g. jäsenten).

• Words ending in -l, -n, -r

• Singular forms: basic form plus -i-
• Singular partitive: basic form plus -iA
• Plural forms: basic form plus -ei-
• Plural partitive: -ejA
• Plural genitive: -ien

• Other foreign word rules