Course grammar - Kurssin kielioppi

3.2. Consonant changes

A consonant change often happens when certain endings are attached to a noun or a verb. Letters k, p and t can shorten, change quality or drop.

The change happens between a strong grade and weak grade. For example a double consonant (strong grade) becomes a single consonant (weak grade)
or a single consonant becomes its weak counterpart or disappears.

Examples:   
Strong grade     Afrikka Africa     katu a street     Hollanti Holland         

Weak grade     Afrikassa in Africa    kadulla on the street   Hollannissa in Holland        

Here are the main consonant change variations:

Strong	Weak	Example
kk	k	Amerikka - Amerikassa
pp	p	Eurooppa - Euroopasta
tt	t	konsertti - konsertin
k	-	Turku - Turussa
p	v	kylpy - kylvyssä
t	d	katu - kadulla
lt	ll	ilta - illalla
nk	ng	Helsinki - Helsingistä
nt	nn	Englanti - Englannissa

CONSONANT CHANGE WITH NOUNS
In Finnish there are two groups of nouns: A and B. The nouns in group A end in a vowel except for e. The nouns in group B end in e or a consonant.

In both groups A and B the singular partitive form has the same grade as the nominative case (basic form). That´s why you don´t have to think about consonant changes when making the singular partitive form.

salaatti salaattia
kastike kastiketta

In group A in the nominative form (basic form) a word has a strong grade, which has to be changed into a weak grade in the genitive and in the locative cases, but not in the illative (where to, inside case). In group A plural basic form is also in a weak grade.

Examples:

Nominative           Genitive                                      Missä?                                   Mistä?  Plural nominative   Nominative Genitive Mihin? (Where to? outside) Missä? (Where? outside) Mistä? (Where from? outside) Plural nominative

kuppi cup                 kupin kupissa  kupista kupit   katu street kadun kadulle kadulla kadulta kadut

sänky bed sängyn sängyssä sängystä sängyt   pöytä table pöydän pöydälle pöydällä pöydältä pöydät

In both groups A and B in the illative form (where to) a word is in a strong grade.
Mihin?                  kuppiin                     sänkyyn                kastikkeeseen


CONSONANT CHANGE WITH VERBS
In verb type 1, the infinitive (basic form) is always in a strong grade, which with most personal endings changes to a weak grade.
Only the 3rd person singular and plural forms stay in the strong grade.

Examples:
nukkua to sleep                                         tietää to know               
minä nukun                                                minä tiedän
sinä nukut                                                   sinä tiedät
hän nukkuu                                               hän tietää
me nukumme                                             me tiedämme
te nukutte                                                   te tiedätte
he nukkuvat                                              he tietävät

Note that the change takes place in the final syllable boundary of the word:
hat-tu - ha-tut → tt changes to t because consonants occur at the final syllable division.
opet-ta-ja - opet-ta-jat → no change because t-consonants do not occur at the final syllable division.