Survival Finnish Online 2.12.-30.12.2020

A consonanat 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

A weak grade is used when the case or personal ending is attached to the word and it is
1. a single consonant: -n or -t (tyttö - tytön girl - girl's, tyttö - tytöt girl girls, ottaa - otan to take - I take)
2. a combination of two consonants and a vowel: -ssa, -sta, -lla, -lta, -lle, -mme, -tte 
   (kauppa - kaupassa shop - in a shop, ottaa - otamme to take - we take).

A strong grade is used when the case or personal ending is attached to the word and it is
1. a vowel: (salaatti - salaattia salad - some salad, nukkua - nukkuu to sleep - she sleeps)
2. a vowel+consonant: (kauppa - kauppaan shop - to the shop, pankki - pankkiin bank - to the bank)
3. a consonant+vowel+consonant: nukkuvat they sleep, ottavat they take)

Here are the main consonant change variations:

Strong	Weak	Example
kk	k	Amerikka - Amerikassa
pp	p	Eurooppa - Euroopasta
tt	t	konsertti - konsertin
k	ø	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 most cases, in a nominative form (basic form), a word has a strong grade, which has to be changed into a weak grade with a suffix.
Note though, that the partitive and illative (where to) endings do not cause consonant change and the word stays in a strong grade.
Example:
Nominative           kuppi cup                 sänky bed
Genitive                kupin                        sängyn
Partitive                kuppia                      sänkyä
Missä?                 kupissa                    sängyssä
Mihin?                  kuppiin                     sänkyyn

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
sinät 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.