Learn Hardcore Afrikaans: Ek klim van die stoel af.

In Afrikaans, af is a separable verb particle indicating downward movement. The full infinitive is afklim (“to climb down”), but in a present-tense main clause you split it: the verb stem (klim) appears in second position and the particle (af) moves to the very end.

Why are both van and af needed to express “down from” instead of just one of them?

van is a preposition meaning “from,” introducing the source (die stoel). af is a directional particle meaning “down.” You can’t say Ek klim af die stoel because af doesn’t govern a noun phrase by itself. Together van … af literally means “from … down.”

Why is the order van die stoel af and not af van die stoel?

In Afrikaans main clauses with separable verbs, the finite verb (here klim) occupies the second position, the object or prepositional phrase follows, and the particle goes to the clause-final slot. So the structure is:
Subject (Ek) – Verb (klim) – Prepositional phrase (van die stoel) – Particle (af).

Does the verb klim change form with different subjects or tenses?

Present-tense verbs in Afrikaans do not conjugate for person or number. You always say Ek klim, Hy klim, Ons klim, etc. To form the past tense, use het plus the past participle afgeklim: Ek het van die stoel afgeklim.

Can I use 'n instead of die, or leave out the article altogether?

You cannot omit the article. You need a determiner before stoel, so you choose die stoel (the chair) for a specific one or 'n stoel (a chair) for any chair:

Ek klim van die stoel af (“I climb down from the chair”)
Ek klim van 'n stoel af (“I climb down from a chair”)

Can this van … af structure be used with other verbs and objects?

Yes. Any separable verb with af works the same way, and you can replace stoel with other nouns:

Ek spring van die tafel af (“I jump off the table”)
Sy klim van die boom af (“She climbs down from the tree”)
Hulle stap van die bus af (“They step off the bus”)