Learn Hardcore Swahili: Polisi anasimamisha daladala sokoni. - The police officer is stopping the minibus at the market.

anasimamisha is the present-tense, third-person-singular form of the verb simamisha (“to cause to stop”). It breaks down as:
• a- subject marker for “he/she/it”
• -na- present-tense marker (“is …ing”)
• simamisha root, which is the causative of simama (“to stand/stop”)

So anasimamisha literally means “he/she is stopping (something).”

Why did we use the causative form simamisha instead of the basic simama?

simama means “to stand” or “to stop oneself.” The causative extension -ish- turns it into simamisha, “to make stand” or “to stop (someone/something).” Since the police officer is stopping a vehicle, you need the causative.

What are the roles of the prefixes a- and -na- in anasimamisha?

• a- is the subject marker for third-person singular (he/she/it).
• -na- is the marker for present tense (equivalent to English “is doing”).

Together they show that “he/she/it is …” in the present.

How can I tell if polisi is singular or plural, and how does that affect the verb?

polisi belongs to a noun class (class 9/10) that has the same form for singular and plural. You rely on the verb prefix to know the number. In our sentence the prefix a- tells you it’s singular (“a police officer”). If you meant “police officers” (plural), you’d use wa-, giving wanasimamisha.

Why isn’t there an English-style article like “the” before polisi or daladala?

Swahili doesn’t use articles like “a” or “the.” Whether a noun is definite or indefinite is understood from context or can be made explicit with demonstratives (e.g. polisi huyo “that policeman”).

What noun class is daladala, and why doesn’t it change to show plural?

daladala (“minibus/commuter van”) is a reduplicated noun in class 9/10, so its form is identical in singular and plural. Context (or qualifiers like moja “one” or nyingi “many”) tells you how many.

What does sokoni mean, and why isn’t there a preposition like “in” or “at”?

sokoni is the locative form of soko (“market”), created by adding the locative suffix -ni. That single word covers “at the market” (and in many cases “to the market”), so no separate preposition is needed.

Could I say katika soko or kwa soko instead of sokoni?

You can say katika soko to mean “in the market,” but sokoni is more idiomatic for “at/to the market.” kwa soko is uncommon for location in everyday speech.

How would I change the sentence to past tense?

Replace the present-tense marker -na- with the past-tense marker -li-. You get:
Polisi alisimamisha daladala sokoni.

How would I make the sentence negative in the present tense?

Use the present negative pattern:

Change a- to ha-
Replace -na- with -si-
Change the verb’s final -a to -i

That yields:
Polisi hasimamishi daladala sokoni.