Consonant Gradation

01

The Double-to-Single Pattern

The clearest case is a doubled consonant becoming single when an ending is added:

• kk → k: pankki → pankissa (bank → in the bank)
• pp → p: kauppa → kaupassa (shop → in the shop)
• tt → t: matto → maton (rug → of the rug)

02

Single-Consonant Changes

Single consonants alternate too, in less obvious ways:

• t → d: katu → kadun (street → of the street)
• p → v: leipä → leivän (bread → of the bread)
• k → (nothing): jalka → jalan (leg → of the leg; the k drops out)
• nt → nn, mp → mm, nk → ng: antaa → annan (to give → I give)

03

When the Weaker Form Appears

As a rough guide, the weaker form appears when the ending brings a consonant in behind the k, p or t — compare pankki with pankissa, where -ssa has done exactly that. Working it out each time is not the point. What is worth having is the expectation: when a noun takes an ending or a verb changes person, look for k, p and t to shift, and read through the change to the word underneath.

• Tämä on pankki.

  This is a bank. (basic form, strong)

• Olen pankissa.

  I'm at the bank. (ending added, weak)

• pankki on its own, but panki-ssa once the ending arrives
• the stem itself changed — this is why a word can look unfamiliar in a form you have not met

04

It Affects Both Nouns and Verbs

In nouns the change appears between the dictionary form and the case forms; in verbs it appears between different persons.

• tyttö → tytön

  girl → of the girl (tt → t)

• nukkua → minä nukun

  to sleep → I sleep (kk → k)

• tehdä → minä teen

  to do → I do

05

Why It Is Worth Knowing

Gradation is the main reason a Finnish word can be hard to recognise across its forms. Once you know that pankki and pankissa are the same word, a large part of the language's apparent complexity falls away.