1. What is it?
When, by adding an ending, a previously open syllable becomes closed, some consonants change! The form with the changed consonants is called the weak stem. The form with the "harder" consonants is the strong stem.
2. When do you use it?
The endings where consonant gradation may take place are those which begin with two consonants (-ssa/-ssä, sta/-stä, -lla/-llä, -lta/-ltä, -lle, -ksi) or consist of one consonant (-t, -n). It only happens when the consonants are on the border between the last and the previous syllable! That's why keittiö becomes keittiössä, but konsertti becomes konsertissa.
3. Which consonants change?
|Strong||Weak||Example 1||Example 2|
|kk||k||pankki -> pankissa||paikka -> paikat|
|pp||p||kauppa -> kaupassa||kuppi -> kupin|
|tt||t||konsertti -> konsertista||kartta -> kartalle|
|nt||nn||Skotlanti -> Skotlannin||Englanti -> Englannissa|
|nk||ng||kaupunki -> kaupungista||Helsinki -> Helsingin|
|t||d||katu -> kadulla||pöytä -> pöydän|
|k||Ø||polku -> polulta||Turku -> Turussa|
|k||v||luku -> luvulla||puku -> puvusta|
|p||v||kylpy -> kylvyssä||apu -> avulla|
|lt||ll||silta -> sillalta||ilta -> illalla|
|rt||rr||virta -> virrat||kerta -> kerran|
|mp||mm||kampa -> kammassa||ampua -> ammun|
|lki||lje||jälki -> jäljen||kylki -> kyljessä|
|rki||rje||järki -> järjet||särki -> särjet|
If a certain consonant combination is not included in this list, they don't consonant gradate. For example: -ss- is not in the list, so you will never consonant gradate -ss- to -s-.
4. Consonant gradation for verbs
When conjugating verbs, you also need to think of consonant gradation. Eachhas its own rules.
5. Consonant gradation for words of wordtype B
If you are just beginning with learning about consonant gradation, I suggest you skip the next part for now. There are a lot more words of wordtype A (which is what has been described higher on this page). It is important though, that once you have progressed more in your studies, you learn this matter as well. I made a seperate page to explain about wordtype B.