…the doctrine of Pragmatism […] according to which every concept proper (as distinguished from a feeling, image, or percept) is fully interpretable in terms of conceivable conduct…
This quote has been taken from Kenneth Laine Ketner's 1983 reconstruction of Peirce's 'Autobiography'. Ketner identifies the source as "variant pages" of the manuscript.
http://www.commens.org/dictionary/entry/quote-brief-intellectual-autobiography-charles-sanders-peirce-22