Breakdown of Он быстро вытер пыль со шкафа.
он
he / it (for a masculine noun) / it (for a neuter noun)
быстро
fast, quickly
шкаф
cabinet / wardrobe
пыль
dust
Questions & Answers about Он быстро вытер пыль со шкафа.
Why is the preposition со used here instead of just с?
We use со before certain combinations of consonants to make pronunciation easier. Saying с шкафа would force you to pronounce three consonants in a row (с-ш-к), which is difficult. Adding the -о makes it much smoother.
How do we know to use со instead of из to mean 'from' here?
The choice of preposition for 'from' depends on where the object originally was. Because dust settles on the outside surface of the cabinet (на шкаф), taking it off requires с/со. If he were taking something out from inside the cabinet (в шкафу), the sentence would use из шкафа.
The past tense verb вытер (wiped) looks a bit unusual. What is its infinitive?
The infinitive is вытереть (to wipe off or dry). It is a perfective verb, indicating he completely finished the job. In the past tense, the -еть drops off entirely, giving us вытер for a masculine subject. For a feminine subject, it would be вытерла.
Why does пыль (dust) look like it hasn't changed case, even though it's the direct object?