…the principle he called pragmatism, that is, that every concept (in contrast to qualities of feeling, images, experiences, etc.) is definable in terms of a possible purpose of conduct under hypothetical general conditions, and that from this can be deduced the best rule for rendering ideas clear, namely, “Consider what effects that might conceivably have practical bearings we conceive the object of our conception to have: then, our concept of those effects is the whole concept in question.”
This quote has been taken from Kenneth Laine Ketner's 1983 reconstruction of Peirce's 'Autobiography'
http://www.commens.org/dictionary/entry/quote-brief-intellectual-autobiography-charles-sanders-peirce-1