-ton/-tön

1. Formation
A common formation pattern uses the genitive singular stem of a noun, without -n. Word formation also has lexical stem changes, so check unfamiliar derivatives rather than treating this as an exceptionless rule.

• koti (home) → koditon (homeless)
• työ (work) → työtön (unemployed)

Nouns of the kone : koneen class use a long -ee- (kone → koneen → koneeton), whereas nouns of the nalle : nallen class do not (nalle → nallen → nalleton).

2. Vowel Harmony
Following vowel harmony, use -ton for back-vowel words and -tön for front-vowel words and bases containing only neutral e/i vowels.

3. Consonant Gradation
The suffix is added to the same stem used for the genitive singular. This means if the word undergoes consonant gradation, the suffix will appear with the same grade as the genitive form. In examples with ordinary weakening, this is the weak grade (e.g., katto → katoton). For nouns that undergo inverse gradation such as vaate, the suffix is attached to the strong grade (e.g., vaate → vaatteeton).

4. Inflection (The -ttoma- Stem)
When you add further case endings to a -ton/-tön word, oblique cases double the 't' and change the stem to -ttoma- (back vowels) or -ttömä- (front vowels). In the plural partitive, it becomes -ttomia- or -ttömiä-. However, the partitive singular is an exception: it keeps a single 't' and does not use the -ttoma- stem (e.g., rahatonta).

• Nominative: rahaton
• Genitive: rahattoman
• Partitive: rahatonta
• Illative: rahattomaan
• Plural Nominative: rahattomat
• Plural Genitive: rahattomien
• Plural Partitive: rahattomia

5. Derivatives (-uus/-yys and -sti)
Abstract nouns use -uus/-yys, replacing the final a/ä of the inflectional stem: rahattoma- → rahattomuus, työttömä- → työttömyys. Adverbs retain that stem vowel before -sti: uskomattoma- → uskomattomasti (unbelievably).

6. Verbal Use (-maton/-mätön)
When attached to verbs, the suffix attaches to the strong vowel stem of the verb and takes the form -maton or -mätön, creating a negative participle that means something is 'un-done' or 'cannot be done' (e.g., tehdä → strong stem teke- → tekemätön 'undone', uskoa → strong stem usko- → uskomaton 'unbelievable').

7. Adjective or Without-Phrase?
Sokeriton is an adjective and agrees with a noun, as in sokeritonta kahvia. Ilman sokeria is a without-phrase. Neither form by itself makes the absence permanent. English equivalents vary: -less, -free, un-, in-/im-, or a whole phrase; use the established meaning of each word.