Which term is the noun form of the adjective 'necessary'?

• A. Necessity
• B. Necessary
• C. Necessariness
• D. Necessitous

Answer: (A)

Forming a noun from an adjective by adding a suffix is a common way to name the state or quality described by the adjective. For the adjective describing something that must be done or required, the standard noun is formed with -ity, giving necessity. This noun expresses the fact or condition of being necessary or something that is needed.

So, when we talk about the need for something or why something must be done, we refer to its necessity. That’s why necessity is the best fit here. The other forms are not the same kind of word: necessary is the adjective itself; necessitous is another adjective meaning needy; and necessariness exists but is very uncommon and sounds awkward in ordinary use.