Learn Hardcore Swahili: Toka nyumbani mapema asubuhi usije ukachelewa kazini. - Leave home early in the morning so that you don’t end up being late for work.

It’s a common caution/warning pattern meaning “lest you end up being late” or “so that you don’t end up late.” Literally it’s “don’t come and (then) be late,” but in natural English we’d say “so you won’t end up late.”

Why does Swahili use the verb “come” (kuja) in “usije” for this meaning?

Swahili often uses “kuja” in the negative subjunctive plus a consecutive verb to warn against an unwanted result:

usije ukafanya X = “lest you (end up) do(ing) X.” It’s idiomatic. You’re not literally telling someone “don’t come”; you’re warning them against a potential consequence.

What is the “ka-” doing in “ukachelewa”?

“ka-” is the consecutive marker. After an imperative or (negative) subjunctive, it introduces the next action as a subsequent or resulting event. In warnings like this, it implies an undesirable outcome:

usije ukachelewa = “don’t (such that you) then end up late.”

Could we just say “utachelewa kazini” instead of “ukachelewa kazini”?

Yes, but it changes the tone:

usije ukachelewa kazini: softer, cautionary, “lest you end up late.”
la sivyo/vinginevyo utachelewa kazini: more definite threat, “otherwise you will be late.”
or simply utachelewa kazini: a straightforward prediction, “you will be late.”

Is “usije ukachelewa” the only way to express “so that you don’t be late”?

No. Alternatives include:

ili usichelewe kazini = “so that you don’t (be) late to work.”
usichelewe kazini = “don’t be late for work.” (direct prohibition) The “usije uka-” pattern is especially natural for warning about an unintended result.

Break down the sentence word by word, please.

Toka = “leave/come out” (2nd person singular imperative of kutoka).
nyumbani = “at/from home” (nyumba + -ni locative).
mapema = “early.”
asubuhi = “morning; in the morning.”
usije = negative subjunctive of kuja “to come” (u- + -sije).
ukachelewa = u- (you) + ka- (consecutive) + chelewa (“be late”).
kazini = “at (the) work / to work” (kazi + -ni locative).

Why “toka” and not “ondoka”? Are they different?

Both can work here.

toka = “come out/leave (from somewhere).” Common with a place of origin: toka nyumbani.
ondoka = “depart/leave (a place).” Also natural: ondoka nyumbani mapema asubuhi… “toka nyumbani” is the more idiomatic everyday phrasing, but “ondoka” is fine too.

How would I say this to more than one person?

Use plural imperatives and plural agreement:

Tokeni nyumbani mapema asubuhi msije mkachelewa kazini. (tokeni = plural imperative; msije/mkachelewa = 2nd person plural with negative subjunctive + consecutive)

Do we always need “ka-” after “usije”?

In this warning construction, yes—“usije” is normally followed by a verb with the consecutive “ka-” (with the appropriate subject prefix):

usije ukasahau = “lest you forget.”
usije ukalala = “lest you fall asleep.”

Could I replace “usije ukachelewa” with “ili usichelewe”? Any nuance difference?

“Ili usichelewe” is goal-oriented (“so that you don’t…”), often used for plans/instructions. “Usije ukachelewa” is more cautionary and idiomatic for warning against an unwanted consequence. Both are correct; choose based on tone.

Why “nyumbani” and “kazini” end in “-ni”? What does that do?

“-ni” is a locative suffix meaning “at/in/to/from” depending on the verb and context.

nyumbani = at/home/from home (here, toka already means “leave from,” so nyumbani reads as “home”/“from home”).
kazini = at work/to work (with chelewa it idiomatically means “late for work”).

Is “chelewa” transitive? Can I “chelewa something”?

“chelewa” is intransitive: “to be late.” The transitive/causative is “chelewesha” = “to delay/make (someone/something) late.”

Nimechelewa kazini = I am late to work.
Trafiki imetuchelewesha = Traffic has made us late.

Is the word order “mapema asubuhi” fixed? Could I say “asubuhi mapema”?

Both are used. You’ll also hear the set phrase “asubuhi na mapema” (“early in the morning”). “Mapema asubuhi” and “asubuhi mapema” are both natural; the meaning is the same.

Do I need a comma before “usije ukachelewa”?

Optional. Many writers will insert a comma to mark the pause:

Toka nyumbani mapema asubuhi, usije ukachelewa kazini. Speech prosody usually has a slight pause there.

How could I make the command more polite?

Tafadhali toka/ondoka nyumbani mapema asubuhi, usije ukachelewa kazini. Adding “tafadhali” softens it. You can also rephrase as advice:
Ni bora uondoke mapema asubuhi ili usichelewe kazini.