Mary Whiton Calkins,
The Idealist to the Realist
(1911)
“ As an idealist, I agree to check myself in every exuberant denial of the possibility that unknown extra-mental objects exist. But I do not hereby recant my idealism. For the truth is that the hypothetical unknown, extra-mental reality is utterly negligible. Such an x, an utterly unknown extra-mental object, is not the object of physical science, of logic, or of mathematics ”
