Questions & Answers about Ideen er god, men virker den i praksis?
Why is the verb virker used here instead of arbejder for "works"?
In Danish, virker means "works" in the sense of functioning, operating, or being effective. arbejder is only used when referring to a person or animal performing labor or a job. Since an idea does not perform physical labor, you must use virker.
Why is the pronoun den used for "it" instead of det?
The pronoun must match the gender of the noun it replaces. "The idea" is ideen, which is a common gender noun (an en-word). Therefore, you must use den to say "it". If the noun were a neuter word (an et-word) like forslaget (the proposal), you would use det.
In the second clause, why is the verb virker placed before the subject den?
The word men (but) is a coordinating conjunction, which means the clause that follows it is treated as an independent sentence. Because this second clause is a question ("does it work in practice?"), it uses standard interrogative word order: verb first (virker), then subject (den).
Is i praksis a fixed phrase, or would you ever use the definite form and say i praksissen?
i praksis is a fixed expression that translates directly to "in practice" (meaning in reality). You do not use the definite article here. If you were to say i praksissen, it would sound like you are referring to a physical location, such as being inside a doctor's or lawyer's office.