noun
Abstract noun referring to the quality of being logically or naturally unavoidable. Often used in philosophical, scientific, or formal contexts.
歴史の変化にはある種の必然性があると考える人もいる。
Some people believe that historical changes have a certain inevitability.
この結論に至ったのには論理的な必然性がある。
There is a logical necessity that led to this conclusion.
必要性 refers to the degree or quality of being needed or required (practical necessity), while 必然性 refers to logical or natural inevitability.
Compound of 必然 (hitsuzen, 'inevitable') + 性 (-sei, '-ness, -ity'), forming an abstract noun. The exact historical derivation is straightforward from these components.