Learn Dutch: Knipt de schaar stroef, dan koop ik een nieuwe. - If the scissors cut stiffly, then I will buy a new pair.

The verb knippen (to cut) is active, but we are not talking about what the scissors are actively cutting. Instead, this uses the facilitive middle voice: combining an active verb with an adverb of manner (stroef) to describe how an object handles or feels when someone uses it. It essentially means 'If the scissors are stiff to cut with'.

Why does the sentence start with the verb Knipt instead of a conditional word like Als (if)?

In Dutch, you can drop the word als (if) to form a conditional clause by putting the verb in the very first position. This verb-first structure, paired with dan (then) in the main clause, translates to 'If [A], then [B]'. You could also say Als de schaar stroef knipt, dan... but this inversion is highly common and natural.

Why is it de schaar and een nieuwe when English uses plurals ('the scissors', 'a new pair')?

Unlike in English, de schaar (the scissors) is a strictly singular noun in Dutch. Because of this, it takes the singular verb knipt, and when buying a replacement, you just buy een nieuwe (a new one) rather than a 'pair'.

What kind of stiffness does the word stroef describe?