-isha / -esha

The verb extensions -isha and -esha are highly productive and used across all registers of Swahili. Their primary function is to increase the verb's valency by introducing a causer. An intransitive verb becomes transitive, and a transitive verb becomes ditransitive.

1. Vowel Harmony in Action:
For standard Bantu verbs ending in -a, the penultimate vowel dictates the suffix:

• pika (cook) has the penultimate vowel 'i'. It becomes pikisha (make cook).
• soma (read) has the penultimate vowel 'o'. It becomes somesha (make read / educate).

2. Arabic Loan Verbs:
For Arabic Loan Verbs ending in -i, -e, or -u, the final vowel is dropped before adding the causative suffix. Instead of penultimate vowel harmony, the suffix is determined by the dropped vowel: words ending in -i or -u take -isha, and those ending in -e take -esha. The newly formed verb always ends in -a and follows standard Bantu conjugation rules:

• rudi (return) -> drops 'i' -> rudisha (return something / give back)
• jibu (answer) -> drops 'u' -> jibisha (make someone answer)
• kodi (rent) -> drops 'i' -> kodisha (rent out)

Exception: Verbs ending in -au (like sahau or dharau) do not drop their final vowel. Instead, they take the suffix -lisha (e.g., sahaulisha).

3. Deriving Verbs from Nouns and Adjectives:
The causative is frequently used to turn adjectives and nouns into verbs. If the word ends in -a, it follows the standard penultimate vowel rule. If it ends in -i or -u, it takes -isha:

• safi (clean) -> ends in 'i' -> safisha (to clean / make clean)
• sababu (reason) -> ends in 'u' -> sababisha (to cause)
• bora (better) -> ends in 'a', penultimate 'o' -> boresha (to improve / make better)

Exception: Some common adjectives, such as -refu (long/tall), do not drop their final vowel and instead just append -sha (becoming refusha).

4. Exceptions and Other Causatives:
Note that -isha and -esha are not the only causative suffixes. Verbs ending in double vowels usually take -za (e.g., jaa -> jaza). Specifically, verbs ending in -ea or -ia usually drop the final -a and take -za (e.g., ingia -> ingiza, zoea -> zoeza). For verbs ending in -ka or -ta, the final syllable is often replaced by -sha (e.g., ruka -> rusha), and verbs ending in -ta can also replace it with -sa (e.g., fuata -> fuasa). There are also irregular forms.

5. Nuances of Meaning:
Beyond direct causation, these extensions can carry an assistive meaning (helping someone do something) or an intensive meaning (doing something forcefully or thoroughly). Context determines the exact nuance.

Note: Do not confuse the causative with the Applicative -ia or Applicative -ea. The causative means making someone do an action, while the applicative means doing an action for someone.