ku- (ngeli ya 15)

In Swahili, when you want to talk about an action as a concept—like "swimming," "reading," or "cooking"—you use the Infinitive ku-. These infinitive nouns make up Noun Class 15.

Because of Agreement Across the Sentence, any verb that has a Class 15 noun as its subject must take the Class 15 subject marker ku-. This ku-/kw- agreement also applies to adjectives, possessives, and demonstratives modifying the Class 15 noun (e.g., Kusoma huku kwangu kuzuri kunafurahisha, "This good reading of mine is pleasing").

In affirmative verbs, this marker usually occupies the very first slot on the conjugated verb. However, there is an exception for the Habitual hu- tense, which replaces subject markers entirely across all noun classes (e.g., Kusoma huchosha, "Reading usually tires"). In standard indicative negative main clauses, it follows the primary negative prefix ha- to become haku- (e.g., Kusoma hakuchoshi, "Reading is not boring"). In dependent clauses or the subjunctive mood, the negative marker is -si-, making the prefix kusi- (e.g., Kusoma kusiwe kubaya, "Reading should not be bad").

How it attaches:

• Before consonants: It remains ku- (e.g., ku-na-furahisha).
• Before vowels: When a verb root starts with a vowel, the subject marker usually attaches to the tense marker (which typically starts with a consonant), so it naturally remains ku- (e.g., ku-na-andika). It only attaches directly to the verb root in tenses without a tense marker, like the present negative or subjunctive. In these cases, it usually remains ku- for most vowel-initial verbs (e.g., hakuumizi). It becomes kw- before a few irregular verbs like -enda and -isha (e.g., Kupika kwende vizuri), as well as with adjectives, possessives, and the simple present -a- tense (e.g., kwafurahisha, kwangu, kwema).

Don't confuse this ku- with others!
Swahili uses the prefix ku- for several different functions. Do not confuse the Class 15 subject marker with:

• The infinitive marker itself (e.g., kusoma).
• The stress-bearing "dummy" ku- used with Ku- Retention in Short Verbs in certain tenses (e.g., ninakula, alikuja).
• The Second-Person Object -ku-, which comes right before the verb root (e.g., ninakuona). Note that -ku- can also function as the Class 15 or Class 17 object marker!
• The Past Negative -ku-, which is a tense marker. Be careful not to confuse the Class 15 negative present (where ha- is the negative prefix and -ku- is the subject marker, e.g., Kusoma hakuchoshi, "Reading is not boring") with the negative past tense for Class 1 (where ha- is the negative subject marker and -ku- is the past tense marker, e.g., Mtu hakusoma, "The person did not read"). They look identical but function differently!
• The Locative Subject Agreement marker ku- (Class 17), which refers to a general location rather than an action. Note that Class 15 and Class 17 share identical agreement markers across the board (ku-, kw-, huku, kwa, etc.). For example, Kule kuzuri kunafurahisha ("That good place over there is pleasing") uses the exact same agreement pattern as Class 15.