
fordern
to demand
To demand or claim something emphatically, often because one believes one has a right to it.
Die Mitarbeiter fordern eine Gehaltserhöhung von fünf Prozent.
The employees are demanding a five percent pay raise.
to demand / challenge
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to demand
To demand or claim something emphatically, often because one believes one has a right to it.
Die Mitarbeiter fordern eine Gehaltserhöhung von fünf Prozent.
The employees are demanding a five percent pay raise.

to challenge
To require effort, ability, or attention from someone or something; to challenge.
Der neue Job fordert meine ganze Energie.
The new job demands all my energy.

to claim
To have as a negative consequence; to demand as a victim or price. Usually used in connection with accidents or disasters.
Der schwere Sturm forderte mehrere Todesopfer.
The severe storm claimed several lives.
The verb 'fordern' (to demand/challenge) belongs to the word family of the noun 'die Forderung' (demand). A 'Forderung' is what one demands emphatically.
Die Forderung nach besseren Arbeitsbedingungen wurde von allen unterstützt.
The demand for better working conditions was supported by everyone.
When demanding something from someone, the structure is often: 'etwas (Akkusativ) von jemandem (Dativ) fordern' (to demand something from someone). Alternatively, a subordinate clause with 'dass' (that) can follow.
Die Kunden fordern vom Unternehmen eine Entschuldigung.
The customers are demanding an apology from the company.
In the meaning 'herausfordern' (to challenge), the subject is often a task, job, or problem. Typical objects are then abstract things like 'Konzentration' (concentration), 'Kraft' (strength), 'Kreativität' (creativity), or 'Geduld' (patience).
Ein Marathonlauf fordert Ausdauer und mentale Stärke.
Running a marathon demands endurance and mental strength.
This meaning is used almost only in connection with negative events such as accidents, wars, or natural disasters. The subject is the event, and the object is usually 'Opfer' (victims), 'Todesopfer' (fatalities), or 'Leben' (lives).
Der schwere Verkehrsunfall forderte drei Verletzte.
The serious traffic accident left three people injured.
to pass / consist / exist
Fordern means expressing a claim or wish emphatically. Auf etwas bestehen additionally emphasizes that you are holding on to this demand and do not want to give it up despite objections or other offers.

Nach dem schlechten Service fordert die Kundin eine vollständige Erstattung.
After the poor service, the customer demanded a full refund.
Trotz des Gegenangebots besteht die Kundin auf einer vollständigen Erstattung.
Despite the counteroffer, the customer insists on a full refund.