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?