This page covers the last of the single-stop qualitative alternations — a lone p softening to v — together with a cluster that happens to involve p: mp collapsing to mm. They share a page for convenience, but you should hold them apart in your head, because they work by different mechanisms. A lone p between vowels changes into a new sound, v. The cluster mp does something else entirely: the p assimilates to the m in front of it, so the two sounds merge into a long mm. Treat them as two rules that happen to live next door.
p → v: the lone stop softens
A single p between vowels — the strong grade — becomes v when the syllable it begins is closed by an ending:
| Basic form (strong: p) | Genitive (weak: v) | Meaning |
|---|---|---|
| leipä | leivän | bread |
| apu | avun | help |
| tapa | tavan | way, custom, habit |
Leivän kuori oli rapea ja sisus vielä lämmin.
The bread's crust was crispy and the inside still warm.
Sain avun juuri ajoissa, kiitos naapurille.
I got help just in time, thanks to the neighbour.
Opin uuden tavan pitää muistiinpanoja.
I learned a new way of keeping notes.
Note that leipä → leivän keeps its front vowels ei and ä untouched — as always, gradation reshapes the consonant and never the vowels.
The same p → v softening happens inside the clusters lp and rp, where the p turns to v but the l or r stays put:
| Basic form | Genitive | Meaning |
|---|---|---|
| halpa | halvan | cheap |
| kylpy | kylvyn | bath |
| arpi | arven | scar |
Löysin yllättävän halvan lennon Rovaniemelle.
I found a surprisingly cheap flight to Rovaniemi.
Kylvyn jälkeen join kupin kuumaa teetä.
After the bath I drank a cup of hot tea.
Leikkauksesta jäänyt arpi on jo lähes haalistunut.
The scar left by the operation has almost faded already.
As with every alternation, the strong grade comes back the moment the syllable reopens. So apu keeps its p in the partitive apua and the illative apuun, and leipä keeps it in leipää and leipään — the v only appears where a consonant-initial ending closes the syllable. If you find yourself unsure, run the syllable test: closed syllable → v, open syllable → p.
Voisitko antaa apua hetkeksi?
Could you lend a hand for a moment?
mp → mm: full assimilation
The cluster mp behaves completely differently. Instead of the p becoming v, the p is fully assimilated by the m in front of it — it becomes a second m, giving a long mm. There is no v anywhere in sight:
| Basic form (strong: mp) | Genitive (weak: mm) | Meaning |
|---|---|---|
| kampa | kamman | comb |
| rumpu | rummun | drum |
| lampi | lammen | pond |
Kamman piikit katkesivat heti ensimmäisellä käytöllä.
The comb's teeth broke off on the very first use.
Rummun ääni kaikui pitkälle yli järven.
The drum's sound echoed far across the lake.
The lampi trap: two changes in one word
Lampi (pond) is the example to slow down on, because inflecting it fires two changes at once. First, mp assimilates to mm. Second, lampi is an i-noun whose stem vowel shifts from -i to -e (the stem is lamme-). So the genitive is not lampin or lammin but lammen — assimilated consonant and changed stem vowel. The strong grade with the original vowel resurfaces only where the syllable stays open, as in the partitive lampea and the illative lampeen.
| Case | Form | Grade |
|---|---|---|
| Nominative | lampi | strong (mp) |
| Genitive | lammen | weak (mm), e-stem |
| Inessive | lammessa | weak (mm), e-stem |
| Partitive | lampea | strong (mp), e-stem |
| Illative | lampeen | strong (mp), e-stem |
Lammen jää ei vielä kanna edes lasta.
The pond's ice won't hold even a child yet.
Uimme lammessa aina juhannuksena.
We always swim in the pond at midsummer.
Pihan perällä on pieni lampi, jossa asuu sammakoita.
At the back of the yard there's a small pond with frogs living in it.
Common Mistakes
❌ Ostin tuoreen leipän torilta.
Incorrect — a lone p softens to v before the closed syllable: leivän, not *leipän.
✅ Ostin tuoreen leivän torilta.
I bought a fresh loaf of bread at the market.
❌ Tarvitsen apun tämän kanssa.
Incorrect — the verb tarvita takes the partitive, so 'help' here is apua (the strong p stays before the vowel ending); *apun is not a real form.
✅ Tarvitsen apua tämän kanssa.
I need help with this.
❌ Kavan hampaat ovat katkenneet.
Incorrect — mp does not become v; it assimilates to mm: kamman, not *kavan.
✅ Kamman hampaat ovat katkenneet.
The comb's teeth are broken.
❌ Uimme lampissa koko kesän.
Incorrect — two changes: mp → mm and the i-stem shifts to e, giving lammessa, not *lampissa.
✅ Uimme lammessa koko kesän.
We swam in the pond all summer.
Key Takeaways
- A lone p softens to v in a closed syllable: leipä → leivän, apu → avun, tapa → tavan; the same in lp/rp clusters (halpa → halvan, kylpy → kylvyn).
- The cluster mp assimilates fully to mm — a different mechanism: kampa → kamman, never *kavan.
- These are two separate rules that merely share a page — do not let p → v leak into mp words or vice versa.
- lampi fires two changes at once: mp → mm and the i-stem becomes an e-stem, giving lammen, lammessa.
- As always, gradation leaves the vowels alone — leivän keeps its front ei and ä.
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Start learning Finnish→Related Topics
- k → ∅ and the k/j/v AlternationsA2 — The messiest gradation: k vanishes (jalka→jalan), turns to v between u/y (puku→puvun) or j after l/r (jälki→jäljen), plus nk→ng (Helsinki→Helsingin).
- Qualitative Gradation: t → dA2 — Strong t softens to d in a closed syllable — katu→kadun, äiti→äidin, pöytä→pöydän, tietää→tiedän — a sound that barely exists outside gradation.
- Assimilation Types: nk→ng, nt→nn, lt→ll, rt→rrA2 — The cluster gradations where a nasal or liquid swallows the following stop, leaving a geminate: Helsinki→Helsingin, ranta→rannan, silta→sillan, parta→parran.
- Quantitative Gradation: kk→k, pp→p, tt→tA2 — The easy half of gradation: a doubled stop shortens to a single one — kukka→kukan, kauppa→kaupan, katto→katon — with no change in sound quality.
- Gradation in Noun DeclensionB1 — How a noun switches grade case by case: tyttö→tytön→tyttöä→tytössä→tyttöön shows one word holding both grades, decided form by form by open vs closed syllable.