Learn Hardcore Swahili: Watoto walikuwa wakikimbia kwenye korido bila viatu, kwa hiyo mwalimu aliwakumbusha kuvaa viatu. - The children were running in the corridor without shoes, so the teacher reminded them to wear shoes.

wa- = they (again, subject prefix agreeing with watoto)
-kimbia = to run
waka- in wakikimbia is actually wa- (they) + -ki- (a marker often used for continuous/ongoing action in the past) + -kimbia (run).

Together, walikuwa wakikimbia is a common way to express a past continuous:
> They were running.

If you said just walikimbia, that means they ran (a completed action), not an ongoing action in the past.

Why is the subject prefix wa- repeated in walikuwa wakikimbia? Isn’t once enough?

In Swahili, when you use kuwa (to be) with another verb to show continuous action, it is normal to:

Conjugate kuwa for subject and tense: walikuwa (they were)
Then use a second verb in a “dependent” or “-ki-” form, which also needs its own subject prefix: wakikimbia (while they were running / as they were running).

So walikuwa wakikimbia literally has:

walikuwa = they were
wakikimbia = they [were] running (ongoing action)

The repetition of wa- is grammatically required in this construction and sounds natural to native speakers.

What is the function of -ki- in wakikimbia?

The -ki- in wakikimbia is often called the “-ki- tense” or the consecutive/continuous marker. Here, it shows that the action is:

ongoing / continuous at a time in the past
or happening at the same time as something else

In walikuwa wakikimbia, -ki- helps create a past continuous sense, like:

waliendelea kukimbia – they continued to run
walikuwa wakikimbia – they were running (for some time)

So, wakikimbia ≈ while (they were) running / as they ran continuously.

What noun class is watoto, and how does it affect the rest of the sentence?

Watoto (children) is in the M-/WA- noun class:

singular: mtoto (child) – class 1
plural: watoto (children) – class 2

Class 2 takes the wa- agreement for:

Subject prefixes on verbs: wa-
- walikuwa – they were
- wakikimbia – they were running
Object prefixes: wa- (them – people):
- aliwa-kumbusha – he/she reminded them

So you see wa- several times because it agrees with watoto.

What is the meaning and structure of aliwakumbusha?

Aliwakumbusha breaks down as:

a- = he/she (subject prefix, noun class 1, here referring to mwalimu)
-li- = past tense marker
-wa- = them (object prefix for people, agreeing with watoto)
-kumbush- = remind (verb root)
-a = final vowel for the infinitive/finite verb

So aliwakumbusha literally means:

He/she reminded them.

Subject: mwalimu (the teacher – implied by a-)
Object: watoto (the children – expressed by -wa-)

What’s the difference between kumbuka and kumbusha?

kumbuka = to remember (yourself)
- Nilikumbuka. – I remembered.
kumbusha = to remind (to cause someone else to remember)
- Nilimkumbusha. – I reminded him/her.
- Mwalimu aliwakumbusha. – The teacher reminded them.

The -sha/-isha ending often makes a verb causative in Swahili: to cause X to happen.
So: kumbuka → kumbusha (remember → cause to remember = remind).

How does kuvaa viatu work grammatically? Why is there ku- in kuvaa?

Kuvaa is the infinitive form of the verb vaa (to wear, to put on clothes/shoes). The ku- at the beginning is like English “to”:

vaa – wear (verb root)
kuvaa – to wear / wearing

In aliwakumbusha kuvaa viatu:

aliwakumbusha – he/she reminded them
kuvaa viatu – to wear shoes

So the full meaning is:
> …the teacher reminded them to wear shoes.

Kuvaa functions like an English infinitive phrase after “remind”:

remind (someone) to wear shoes.

Why is viatu used, and what noun class is it in?

Viatu (shoes) is in the KI-/VI- noun class:

singular: kiatu – a shoe
plural: viatu – shoes

The prefixes:

singular ki-
plural vi-

In the sentence you just have bila viatu – without shoes. There is no attached verb that needs to agree with viatu, so you only see the noun form itself.

How does bila viatu work? Why not bila ya viatu or something similar?

Bila means without.

Common patterns are:

bila + noun
- bila viatu – without shoes
- bila maji – without water
bila ya + noun – slightly more formal/emphatic, but often interchangeable
- bila ya viatu – also “without shoes”

In everyday Swahili, bila viatu is short and very natural.
If you wanted to say without their shoes, you could say:

bila viatu vyao – without their shoes.

What does kwenye mean, and how does it differ from katika or just kwenda?

Kwenda is a verb (to go), so that’s different.

Kwenge is a preposition meaning roughly:

in
on
at
into / onto (depending on context)

Katika also means in/inside/within, but tends to feel a bit more formal or “neutral”.

In the sentence:

kwenye korido – in the corridor / in the hallway

You could also say:

katika korido – grammatically fine, a bit more formal or book-like.
koridoni – using the locative suffix -ni: in the corridor (this is also common).

Kwenge is very common in spoken Swahili and flexible in meaning.

What is korido? It looks similar to English “corridor”.

Korido is a loanword from English “corridor” (or from another European language via English). It means:

korido – corridor / hallway.

Loanwords like this are very common in Swahili, especially for modern or school-related terms. The noun behaves like a typical noun:

singular: korido
often pluralized as korido or sometimes makorido (depending on speaker/variety).

Here it’s used with kwenye:

kwenye korido – in the corridor.

What does kwa hiyo mean, and how is it different from kwa sababu?

kwa hiyo = so / therefore / as a result
- It introduces a result or consequence.
kwa sababu = because
- It introduces a reason / cause.

In the sentence:

Watoto walikuwa wakikimbia kwenye korido bila viatu, kwa hiyo mwalimu aliwakumbusha kuvaa viatu.
– The children were running in the corridor without shoes, *so the teacher reminded them to wear shoes.*

If you were using kwa sababu, the structure would change, e.g.:

Mwalimu aliwakumbusha kuvaa viatu kwa sababu walikuwa wakikimbia kwenye korido bila viatu.
– The teacher reminded them to wear shoes *because they were running in the corridor without shoes.*

Why is the verb with mwalimu just aliwakumbusha, with a- and not wa-?

Verbs agree with the subject noun class. Here:

mwalimu (teacher) is singular, in the M-/WA- class:
- singular subject prefix: a- (he/she)
- plural (walimu – teachers): wa- (they)

In the sentence, there is one teacher, so:

a-li-wa-kumbusha
- a- = he/she (the teacher)
- -wa- = them (the children)
- -kumbusha = remind

If it were multiple teachers (walimu), you would have:

walimu waliwakumbusha kuvaa viatu.
- wa-li-wa-kumbusha – they reminded them.

Is the comma before kwa hiyo required, and does it change anything grammatically?

The comma before kwa hiyo is punctuation, not grammar. It simply separates:

The first clause: Watoto walikuwa wakikimbia kwenye korido bila viatu
From the result clause: kwa hiyo mwalimu aliwakumbusha kuvaa viatu

You can see a similar structure in English:

The children were running in the corridor without shoes, *so the teacher reminded them to wear shoes.*

Spoken Swahili doesn’t “have” commas, of course, but the pause you naturally make is represented by the comma in writing. The grammar is the same with or without it; the comma just improves readability.