Necessary vs. Inevitable — What's the Difference?

Needed or required

Certain to happen; unavoidable

Unavoidably determined by prior conditions or circumstances; inevitable

A situation that is unavoidable

Logically inevitable

Impossible to avoid or prevent; certain to happen.

Required by obligation, compulsion, or convention

Invariably occurring or appearing; predictable

Something indispensable.

To avoid or prevent.

Required, essential, whether logically inescapable or needed in order to achieve a desired result or avoid some penalty.

Or always happening.

Unavoidable, inevitable.

Something that is predictable, necessary, or cannot be avoided.

(obsolete) Determined, involuntary: acting from compulsion rather than free will.

Not evitable; incapable of being shunned; unavoidable; certain.

A place to do the "necessary" business of urination and defecation: an outhouse or lavatory.

Irresistible.

(obsolete) Necessity.

An unavoidable event;

Such as must be; impossible to be otherwise; not to be avoided; inevitable.

Incapable of being avoided or prevented;

Impossible to be otherwise, or to be dispensed with, without preventing the attainment of a desired result; indispensable; requisite; essential.

Invariably occurring or appearing;

Acting from necessity or compulsion; involuntary; - opposed to free; as, whether man is a necessary or a free agent is a question much discussed.

A thing that is necessary or indispensable to some purpose; something that one can not do without; a requisite; an essential; - used chiefly in the plural; as, the necessaries of life.

A privy; a water-closet.

Such things, in respect to infants, lunatics, and married women, as are requisite for support suitable to station.

Anything indispensable;

Absolutely essential

Unavoidably determined by prior circumstances;