The Standard Swahili infinitive is a single word built with class-15 ku- before a verb stem: ku-som-a → kusoma “to read/reading.” It is nonfinite: it does not itself locate the event in time or agree with a person as subject, although it can contain an object marker and derivational material.
English learners often treat ku as a detachable translation of to. It is instead a prefix inside the Swahili word, and the same class-15 form can translate an English infinitive, gerund, or action noun.
The infinitive is also the normal citation form used in dictionaries and vocabulary lists. Learning kusoma rather than an isolated soma preserves the noun-class prefix while still letting you identify the stem -soma. In actual sentences, do not add finite subject or TAM material unless the form has ceased to be an infinitive.
The basic build
| Analytic build | Infinitive | Meaning |
|---|---|---|
| ku-som-a | kusoma | to read / reading |
| ku-andik-a | kuandika | to write / writing |
| ku-fungu-a | kufungua | to open / opening |
| ku-jib-u | kujibu | to answer / answering |
| ku-sameh-e | kusamehe | to forgive / forgiving |
| ku-i-som-a | kuisoma | to read it (class 9) |
| ku-mw-ambi-a | kumwambia | to tell him/her |
| ku-ji-funz-a | kujifunza | to learn (teach oneself) |
The object slot follows ku- in ku-i-som-a. The reflexive -ji- occupies that same slot in kujifunza. All finished forms are written solid; hyphens belong only in grammatical analysis.
Nataka kusoma taarifa hiyo kabla ya mkutano.
I want to read that report before the meeting.
Asha alisahau kuifunga milango ya nyuma.
Asha forgot to lock the back doors.
The finite verbs nataka and alisahau carry subject and TAM. Kusoma and kuifunga name the dependent actions without copying those markers.
Preserve the stem's final vowel
Regular Bantu stems commonly end in -a, but many borrowed verbs end in -i, -u, or -e. Infinitive ku- does not normalize them.
Ni muhimu kujibu barua pepe kabla ya Ijumaa.
It is important to answer the email before Friday.
Alikataa kusamehe kosa ambalo halikuelezwa.
She refused to forgive a mistake that had not been explained.
The forms are ku-jib-u and ku-sameh-e, not kujiba or kusameha. This is the same lexical final-vowel distinction used throughout the verb stem system.
Vowel-initial stems and kw-
The spelling before a vowel must be learned from the established infinitive. Standard kwenda “to go” contains kw- rather than kuenda, and kwisha “to finish/be exhausted” is a common contracted form alongside kuisha. These familiar forms reflect ku- before a vowel-initial base.
Tunapanga kwenda Morogoro mwishoni mwa mwezi.
We are planning to go to Morogoro at the end of the month.
Maji yamekaribia kwisha kwenye tangi.
The water in the tank is nearly exhausted.
Do not extend kw- mechanically to every written vowel-initial stem. Standard orthography preserves ku- in common forms such as kuandika, kuanza, kuingia, kuona, and kuuliza.
Kuandika kwa mkono kunanisaidia kukumbuka.
Writing by hand helps me remember.
Wageni walianza kuingia ukumbini saa moja jioni.
The guests began entering the hall at seven in the evening.
There is no safe sound-only shortcut for the whole lexicon. Memorize kwenda as the standard form and recognize regional (informal) kuenda, while using dictionary spelling for other vowel-initial verbs.
Infinitive versus finite template
Compare the same root in a finite statement and an infinitive:
Mariam anaandika muhtasari sasa.
Mariam is writing the summary now.
Mariam anataka kuandika muhtasari kesho.
Mariam wants to write the summary tomorrow.
Finite a-na-andik-a has class 1 subject a- and present -na-. Nonfinite ku-andik-a replaces that outer inflection with class-15 ku-. It does not mean present, past, or future by itself; kesho and anataka locate the intended writing.
Negation likewise uses its own infinitival pattern kuto-, not a negative finite subject prefix:
Aliamua kutosaini mkataba mpaka wakili ausome.
He decided not to sign the contract until a lawyer reads it.
The build is ku-to-sain-i → kutosaini. Compare finite hakusaini “he did not sign,” which contains negative past morphology and an expressed subject. Negative infinitives receive fuller treatment on negative infinitives.
Class 15 is grammatical, not just spelling
Infinitival ku- is also a noun-class prefix. When an infinitive acts as a clause subject, a following finite verb can agree with it using class-15 ku-.
Kusafiri usiku kunahitaji maandalizi mazuri.
Traveling at night requires good preparation.
The first ku- forms the action noun kusafiri. The second is subject concord in ku-na-hitaji. English traveling hides this noun-class relationship; Swahili displays it twice. See the infinitive as a class-15 noun.
This also explains why infinitival ku- is not simply an English-style particle. It assigns the whole action expression to a concord class. The same spelling can occur in other parts of Swahili grammar, especially class-17 locative concord, but the structure distinguishes them: infinitival ku- is immediately followed by a verbal stem and builds the action word.
Common Mistakes
Writing ku as a separate word
❌ Ninataka ku soma ujumbe wako.
Incorrect spelling — infinitival ku- is attached to the stem.
✅ Ninataka kusoma ujumbe wako.
I want to read your message.
Adding subject and TAM to the dependent action
❌ Tunajaribu tunafungua faili hiyo.
Incorrect for one control construction — the attempted action should be infinitival.
✅ Tunajaribu kufungua faili hiyo.
We are trying to open that file.
Changing a non-a stem
❌ Aliahidi kujiba leo.
Incorrect for ‘to answer’ — kujibu retains final -u.
✅ Aliahidi kujibu leo.
He promised to answer today.
Applying kw- to every vowel-initial root
❌ Wameanza kwandika majina yao.
Incorrect Standard spelling — kuandika preserves ku-.
✅ Wameanza kuandika majina yao.
They have begun writing their names.
Key Takeaways
- Attach class-15 ku- directly to the stem and preserve its lexical final vowel.
- Object and reflexive markers follow ku- inside the infinitive.
- Learn kwenda and kwisha, but do not turn every vowel-initial ku- into kw-.
- An infinitive has no person or TAM of its own; its context supplies the interpretation.
Now practice Swahili
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Start learning Swahili →Related Topics
- Optative na + SubjunctiveC1 — Use independent na with a subjunctive for elevated blessings, wishes, and injunctions, while distinguishing it from ordinary and/with and bound present -na-.
- The Infinitive as a Class-15 NounB1 — Use ku- infinitives as subjects, objects, and predicate expressions, with class-15 agreement and English gerund translations.
- Verb Root, Extended Stem and InfinitiveA2 — Relate dictionary ku- forms to bound roots, derivationally extended stems, and fully inflected Swahili verb words.
- Class 15: ku- Infinitive NounsA2 — Use Swahili ku- infinitives as verbal nouns, recognize their ku- agreement, and distinguish nominal infinitives from finite verbs and deceptive ku-initial nouns.