From "Introduction, Association of Ideas," c.1893, from _Grand Logic_, Widener IB2-1
CP 7.440.
"Experience is double, as much as reality is. That is, there is an _outward_ and an _inward experience_. Under the latter head ought particularly to be reckoned a mathematical experience, not usually so called, which has compelled the development of pure thought to take a determinate course." -- Charles Sanders Peirce
Cap tip Ben