In a paper published in the Proceedings of the American Academy of Arts and Sciences for 1867 May 14, I defined the three ways in which an idea can be mentally isolated from another. They [are] Dissociation, Prescission, and Discrimination. [—] Discrimination consists in logically supposing the former idea to be absent though the latter is present. Thus, I can discriminate color from space, since I can logically suppose that there is a space that is uncolored.
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