ratio cognoscendi
/ˈreɪʃɪəʊ ˌkɒɡnəˈsɛndʌɪ/ /ˈrɑːtɪəʊ ˌkɒɡnəˈsɛndi/Philosophy
noun
That by reason of which knowledge of something is possible; that by reason of which something is known to exist.
Origin
Mid 19th century; earliest use found in William S. Hamilton (1788–1856), philosopher. From post-classical Latin ratio cognoscendi from classical Latin ratiō + cognōscendī, genitive of the gerund of cognōscere to know.