Learn Hardcore German: Stell den Stuhl nicht im Weg ab, sonst stolpere ich. - Don’t put the chair in the way, otherwise I’ll trip.

You’ll also see this with many verbs: Komm! / Komme!, Geh! / Gehe! (though the short form is usually more natural in everyday German).

What does ab do in abstellen? Why is it separated?

abstellen is a separable-prefix verb: ab- + stellen. In main clauses, the prefix often moves to the end:

Stell ... ab. In infinitives and subordinate clauses, it stays attached:
... den Stuhl nicht im Weg abzustellen
..., weil du den Stuhl im Weg abstellst

Meaning-wise, abstellen commonly means to put something down / place something somewhere (and leave it there), or to park (a car/bike).

Why is it den Stuhl (accusative)?

Because stellen (and abstellen) takes a direct object: you are placing the chair somewhere. Direct objects are typically in the accusative:

den Stuhl = accusative masculine singular of der Stuhl

If it were “the chair is standing,” you’d use stehen (no direct object in that sense): Der Stuhl steht im Weg.

Why is it im Weg and not auf dem Weg? What’s the difference?

im Weg literally means “in the way” = blocking, obstructing.

Der Stuhl steht im Weg. = The chair is in the way.

auf dem Weg usually means “on the way” in the sense of “en route” or “on the path/road”:

Ich bin auf dem Weg nach Hause. = I’m on my way home. It can also be literal “on the path,” but im Weg is the idiomatic choice for “in the way.”

What exactly is sonst doing here?

sonst here means “otherwise / or else”. It introduces a consequence if the command isn’t followed:

..., sonst stolpere ich. = ..., otherwise I’ll trip.

It’s very common after an imperative: Mach das nicht, sonst ...

Why is it stolpere ich and not ich stolpere?

Because sonst occupies the first position in the clause, triggering verb-second (V2) word order in German. So the finite verb comes next:

sonst stolpere ich not
sonst ich stolpere (wrong)

You could also say:

Sonst stolpere ich darüber. (adding darüber = “over it”)

Is the second clause missing a word like darüber (“over it”)?

It’s not required. German often leaves it implicit when it’s obvious what you’d trip over. Adding it can make it more explicit:

..., sonst stolpere ich. (natural, general)
..., sonst stolpere ich darüber. (more specific: over it/over that)

Why is there a comma before sonst?

Because the sentence contains two main clauses: an imperative clause and a second clause giving the consequence. German normally separates such clauses with a comma, especially when the second clause is introduced by a connector like sonst:

Stell ..., sonst ...

Could I replace nicht with kein here?

No. nicht negates the action (don’t place/park it there). kein negates a noun phrase (“no chair”), which doesn’t fit here.

Correct: Stell den Stuhl nicht im Weg ab.
Incorrect/odd: Stell keinen Stuhl im Weg ab. (This would mean “Don’t put any chair in the way,” which is possible but changes the meaning and sounds less direct in this context.)

Why is it Stell ... ab and not Stell ... hin or Stell ... weg?

They’re related but not identical:

abstellen: put/place something somewhere and leave it there; also “park.” Very neutral/common.
hinstellen: “put (it) there” with emphasis on the destination (hin- = “towards there”). Often implies a specific spot.
wegstellen: “put away / move out of the way,” focusing on removing it.

So if you specifically want “out of the way,” you might say:

Stell den Stuhl weg, sonst stolpere ich.

Is Stell addressed to one person? How would it change for Sie or ihr?

Yes, Stell is the du imperative (one person, informal).

Other forms:

ihr (plural informal): Stellt den Stuhl nicht im Weg ab, sonst stolpere ich.
Sie (formal): Stellen Sie den Stuhl nicht im Weg ab, sonst stolpere ich.

What does abstellen mean in other contexts? Could it be confusing?

It can have a few common meanings depending on context:

to put down / set aside / place somewhere: Stell die Tasche hier ab.
to park (a vehicle): Ich stelle das Fahrrad dort ab.
to turn off / shut off (a device) (less central but used): Stell den Motor ab.

Here, with den Stuhl and im Weg, it clearly means “put/place (the chair) somewhere so it’s not blocking.”

Could the sentence also be phrased with weil, like “because I’ll trip”?

Yes, but it changes the structure:

Stell den Stuhl nicht im Weg ab, weil ich sonst stolpere. Now weil introduces a subordinate clause, so the verb goes to the end:
..., weil ich sonst stolpere. (Here sonst can still appear, but it no longer triggers V2 inside the weil-clause.)

Is stolpere ich present tense, future, or something else?

It’s present tense, but German often uses the present to talk about near-future results:

..., sonst stolpere ich. = “... or else I’ll trip.”

You can make the future explicit, but it’s usually unnecessary:

..., sonst werde ich stolpern. (less natural in everyday speech)