Stephen C. Pepper published _Concept and Quality: A World Hypothesis_ in 1966 (when he was 75 years old!) The volume includes a series of papers associated the [Paul Carus Lecture](https://www.apaonline.org/page/carus) 1964, of three lectures over three days.
* A softcopy version of the book can be borrowed, by the hour, [on the Internet Archive](https://archive.org/details/conceptqualitywo0000pepp)
Selectivism is presented as a _World Hypothesis_, following the four adequate hypotheses in World Hypotheses: A Study in Evidence (1942).
* Main points on the book are discussed in Bill J. Harrell (2004) [_Five World Hypotheses: A primer on Stephen C. Pepper's Epistemologoical System with Illustrations from the Arts, Humanities, Social, and Natural Sciences_](https://web.archive.org/web/20070818234951/http://people.sunyit.edu/~harrell/Pepper/pep_wh-select01.htm) .