Let us conceive, then, of an algebra in which the symbols x, y z etc. admit indifferently of the values 0 and 1, and of these values alone The laws, the axioms, and the processes, of such an Algebra will be identical in their whole extend with the laws, the axioms, and the processes of an Algebra of Logic. Difference of interpretation will alone divide them. Upon this principle the method of the following work is established.
p. 37; Cited in: William Torrey Harris (1879) The Journal of Speculative Philosophy, p. 109 - An Investigation of the Laws of Thought (1854)