ratio cognoscendin.

1663 E. Waterhouse Fortescutus Illustratus vii. 132 This is Etymology in the general and large capacity of the word; yet in Grammar, Etymology is taken for the ratio cognoscendi casuum discrimina, having relation to all parts of speech, and so it is here to be taken as our Chancellour refers it to Grammar, and makes it a part of it.

1698 J. Sergeant Non Vltra 20 These First Truths have all the Requisites that can be imagin'd for a Ratio cognoscendi Veritatem, or a Rule of Truth.]

1830 W. Hamilton in Edinb. Rev. 52 178 The existence of external things, which is given only through their intuition, it admits; the intuition itself, though the ratio cognoscendi, and to us therefore the ratio essendi of their reality, it rejects.

1865 S. H. Hodgson Time & Space vii. 488 Now both the cause, or ratio existendi, and the reason, or ratio cognoscendi, in every particular case must be given by actual experience.

1890 W. James Princ. Psychol. I. x. 337 But if the brand is the ratio cognoscendi of the belonging, the belonging, in the case of the herd, is in turn the ratio existendi of the brand.

1903 G. E. Moore Principia Ethica iv. 127 Kant..admits that Freedom is the ratio essendi of the Moral Law, whereas the latter is only ratio cognoscendi of Freedom.

1972 Evangelical Q. 44 241 These activities compose the ratio cognoscendi of the pardoning grace of God; they make us aware of God's activity which is the ratio essendi that calls forth man's response.

2005 W. J. Wainwright Relig. & Morality vii. 119 A is the ratio cognoscendi of B if B is known through A.