-isha

The causative extension is highly frequent and fully productive in everyday spoken Swahili. It is a fundamental building block of the language.

1. Adding a Causer
The primary function is to indicate that a subject causes someone or something else to perform an action or enter a state.

• Soma (read) → Somesha (educate / sponsor education). Note: The standard word for "teach" is fundisha.
• Kumbuka (remember) → Kumbusha (make remember / remind)

2. Intensive Meaning
Beyond strict causation, this extension frequently carries an intensive meaning, indicating that an action is done thoroughly, forcefully, or to completion.

• Shika (hold) → Shikisha (fasten / hold firmly)

3. Morphological Rules for -isha / -esha
The -isha suffix is used if the last vowel of the root is a, i, or u. If the last vowel of the root is e or o, the suffix becomes -esha.

• Lipa (pay) → Lipisha (make pay / charge) and Lipiza (exact / force a return, e.g., lipiza kisasi - take revenge)
• Rudi (return) → Rudisha (make return)
• Andika (write) → Andikisha (make write / register)

Note on Consonant Mutation: Due to historical sound changes, verbs where -ka or -ta is a stative extension often drop this final syllable and take -sha directly (e.g., chemka → chemsha). However, active verbs where -ka is part of the root take the regular suffix (e.g., andika → andikisha). Some verbs ending in -ta mutate to -sa instead (e.g., takata [be clean] → takasa [cleanse]). Other mutations are caused by a "short causative" suffix -y- blending with the preceding consonant. For example, verbs ending in -na often change to -nya (e.g., on-a + y → onya), and verbs ending in -wa often change to -vya (e.g., lew-a + y → levya).

4. Denominal and Deadjectival Use
The causative is also the primary way Swahili turns nouns and adjectives into verbs. For Arabic loanwords or nouns ending in vowels (like safi, sababu, or bora), the final vowel is generally dropped and replaced by the -isha or -esha suffix. The choice between -isha and -esha is dictated by the remaining root (penultimate) vowel, following the standard vowel harmony rules.

• Safi (clean [adj]) → Safisha (to clean [verb]) (root vowel a takes -isha)
• Bora (better / excellent [adj]) → Boresha (to improve [verb]) (root vowel o takes -esha)

5. The -za / -eza / -iza Variants
Another primary causative suffix is -za. Verbs ending in double vowels typically take -za by dropping the final vowel of the verb (the -a) (e.g., kimbia → kimbiza, not kimbiaza). The variants -eza and -iza are used for certain consonant-ending verbs.

• Jaa (be full) → Jaza (fill)
• Pungua (decrease) → Punguza (reduce)

6. Object Agreement with Causees
Because the causative increases valency (adds a participant to the action), it almost always requires an animate object prefix when the causee (the one being made to do the action) is a person or animal (e.g., Mwalimu aliwasomesha wanafunzi - The teacher taught the students).

7. Passive Causatives
Causative verbs can easily be made passive by adding -wa to the end (forming -ishwa or -eshwa).

• Andikisha (register) → Andikishwa (be registered)

Longer and Lexical Causatives:
The simple -isha/-esha model is most useful for suitable consonant-final roots. Other stems need learned forms: jua → julisha (know → inform) and kula → kulisha (eat → feed). The latter contains infinitive ku- plus derived -lisha; kula is not a two-vowel root. Compare lala → laza (lie/sleep → lay down) and penda → pendeza (like → please). Do not manufacture these by appending -isha to the entire infinitive.