The Commens Dictionary
Quote from ‘Lowell Lectures. 1903. Lecture 5. Vol. 1’
An ens rationis may be defined as a subject whose being consists in a Secondness, or fact, concerning something else. Its being is thus of the nature of Thirdness, or thought. Any abstraction, such as Truth or Justice, is an ens rationis. That does not prevent Truth and Justice from being real powers in the world without any figure of speech.
MS [R] 469:8
‘Ens Rationis’ (pub. 08.01.15-16:05). Quote in M. Bergman & S. Paavola (Eds.), The Commens Dictionary: Peirce's Terms in His Own Words. New Edition. Retrieved from http://www.commens.org/dictionary/entry/quote-lowell-lectures-1903-lecture-5-vol-1.