Turkish Consonant Mutation: The 'Ketçap' (K-T-Ç-P) Suffix Rule Explained

Some Turkish words seem to change spelling when you add an ending: kitap (book) becomes kitabı (the book, as object), çocuk (child) becomes çocuğum (my child). This is consonant softening (ünsüz yumuşaması), and it is completely predictable in its main pattern: the voiceless stops p, ç, t, k at the end of a word become voiced b, c, d, ğ/g when a vowel-initial suffix follows. A handy reminder is the word ketçap (ketchup), which contains all four letters. This guide covers the rule, which words it applies to, the exceptions, and the mirror-image rule of consonant hardening.

The four pairs

After a vowel, k becomes the soft ğ; after n, it becomes an ordinary g: renk → rengi, denk → dengi. Loanwords ending in g also turn it into ğ: psikolog → psikoloğu, katalog → kataloğu.

When does it happen?

Two conditions must both be met:

1. The word ends in p, ç, t or k.
2. The suffix that follows begins with a vowel.

Common vowel-initial suffixes that trigger softening:

Consonant-initial suffixes never cause softening: kitaplar (books), kitapta (in the book), kitapsız (without a book), çocukluk (childhood). The same principle explains the ğ in many verb forms: the future and participle suffixes end in k, which softens before a vowel: gelecek + im → geleceğim (I will come), okuduk + um → okuduğum (that I read). See possessive suffixes and the accusative case for the endings you will use most.

Verbs: t → d in a few stems

Four very common verbs soften their final t before a vowel: gitmek (go) → gidiyorum, gider, gidecek; etmek (do) → ediyor, eder; tatmak (taste) → tadıyor; gütmek (herd) → güdüyor. Most other verbs keep their t: bitmek → bitiyor, satmak → satıyor.

Exceptions: when the consonant stays

1. Most one-syllable words

But some one-syllable words do soften, and they are frequent: renk → rengi (colour), kalp → kalbi (heart), dert → derdi (trouble), yurt → yurdu (homeland, dormitory), tat → tadı (taste), uç → ucu (tip), dip → dibi (bottom), kap → kabı (container), çok → çoğu (most of it), dört → dördü (four of them).

2. Many loanwords

Many words of Arabic or French origin keep their consonant: hukuk → hukuku (law), sanat → sanatı (art), saat → saati (hour), devlet → devleti (state), millet → milleti (nation), ahlak → ahlakı (morals), bisiklet → bisikleti (bicycle), otomat → otomatı (vending machine). There is no shortcut here: when you learn a loanword, learn its accusative too, or check it in the suffix deconstructor.

How to check a word: the dictionary entry

Turkish dictionaries, including the TDK’s Güncel Türkçe Sözlük, show the behaviour of each word in its entry: kitap, -bı means the accusative is kitabı (it softens), while top, -pu means topu (it doesn’t). When you add a new noun ending in p, ç, t or k to your vocabulary list, write its accusative next to it, for example ağaç (ağacı), süt (sütü), saat (saati), and the exceptions will take care of themselves.

3. Proper names in writing

Names keep their spelling and take an apostrophe: Ahmet’e, Mehmet’in, Zonguldak’a. In speech, many people do soften them (“Ahmed’e”), but the written form never changes.

The opposite rule: consonant hardening

The reverse also happens: after a voiceless consonant, a suffix beginning with c or d hardens to ç or t (and, in a few derivational suffixes, g to k: çalış + gan → çalışkan, hard-working). The voiceless consonants are f, s, t, k, ç, ş, h, p, remembered by the phrase FıSTıKÇı ŞaHaP (“Şahap the pistachio seller”).

Note that one word can show both rules: kitap + ta → kitapta (hardening), kitap + ı → kitabı (softening).

Example sentences

1. Kitabını unutma! — Don’t forget your book!
2. Çocuğum yedi yaşında. — My child is seven years old.
3. Ağaca bir kuş kondu. — A bird landed on the tree.
4. Bu kâğıdı imzalayın, lütfen. — Please sign this paper.
5. Dolabın içinde ne var? — What’s in the cupboard?
6. İlacını içtin mi? — Did you take your medicine?
7. En sevdiğin renk ne? — Rengi mavi. — What’s your favourite colour? – (Its colour is) blue.
8. Sokakta çok gürültü var. — There’s a lot of noise in the street.
9. Topu bana at! — Throw me the ball!
10. Kalbim hızlı atıyor. — My heart is beating fast.
11. Yarın İzmir’e gidiyorum. — I’m going to İzmir tomorrow.
12. Sütü buzdolabına koydum. — I put the milk in the fridge.
13. Bu kitaptan çok şey öğrendim. — I learned a lot from this book.
14. Saati duvara astım. — I hung the clock on the wall. (saat → saati, no softening)
15. Dördüncü kattayız. — We’re on the fourth floor.
16. Mehmet’e söyledim. — I told Mehmet.

Common mistakes

• Softening before a consonant-initial suffix: ❌ kitablar, çocuğlar / ✅ kitaplar, çocuklar.
• Not softening before a vowel: ❌ kitapı, çocukum / ✅ kitabı, çocuğum.
• Softening one-syllable words: ❌ tobu, südü / ✅ topu, sütü.
• Softening names in writing: ❌ Ahmed’e / ✅ Ahmet’e.
• Forgetting hardening: ❌ kitapda, yapdı / ✅ kitapta, yaptı.

Mini-exercise

Add the suffix and apply softening or hardening where needed.

1. köpek + i (accusative) → ?
2. ağaç + da → ?
3. dolap + ım → ?
4. top + a → ?
5. kanat + ı → ?
6. renk + ler → ?
7. gitmek → (ben) present continuous → ?
8. hukuk + u → ?

Answers: 1. köpeği 2. ağaçta 3. dolabım 4. topa 5. kanadı 6. renkler 7. gidiyorum 8. hukuku

Next steps

Try the endings on your own words with the harmony calculator, then see how softening interacts with buffer letters and vowel harmony.