Mid 19th century; earliest use found in Shadworth Hollway Hodgson (1832–1912), philosopher. From post-classical Latin ratio existendi from classical Latin ratiō + existendī, genitive of the gerund of existere.
Definition of ratio existendi in US English:
ratio existendi
noun
Philosophy
= ratio essendi.
Origin
Mid 19th century; earliest use found in Shadworth Hollway Hodgson (1832–1912), philosopher. From post-classical Latin ratio existendi from classical Latin ratiō + existendī, genitive of the gerund of existere.