Necessity is an unavoidable fact of life, and is often described in many different ways. COMPULSION (10 letters) is an overwhelming force that compels someone to do something, while DESIDERATUM (11 letters) is a desired thing or quality. IMPERATIVE (10 letters) is an urgent command or REQUIREMENT, and CONSTRAINT (10 letters) is a restriction or limitation. PRECONDITION (12 letters) is a condition that MUST be fulfilled before something else can happen, and INEVITABILITY (13 letters) is the quality of being certain to happen. PREDICAMENT (11 letters) is a difficult situation, DURESS (6 letters) is a state of being forced to do something, and CAUSE (5 letters) is the reason for something happening. DUTY (4 letters) is an obligation or responsibility, DESIRE (6 letters) is a strong feeling of wanting something, OCCASION (8 letters) is an event or situation, MUST (4 letters) is an obligation, NEED (4 letters) is a REQUIREMENT, REQUISITE (9 letters) is something necessary, REQUIREMENT (11 letters) is a demand or condition, and mother of invention (17 letters) is a phrase used to describe the idea that necessity is the mother of invention.