1. Macmillan, Barclay and Macmillan, Cambridge 1847 (referred to hereafter as MAL). Reprinted in Collected Logical Works by George Boole. Vol. I. Studies in Logic and Probability, Rush Rhees (ed.), The Open Court, La Salle Ill. 1952 (referred to hereafter as CLW), pp. 45–124. MAL was recently reprinted in From Kant to Hilbert: A Source Book in the Foundations of Mathematics, W.B. Ewald (ed.), Clarendon Press, Oxford 1996, vol. I, pp. 451–509, and also as a monograph (with an introduction by J. Slater) by Thoemmes Press, Bristol 1998. References are to the original 1847 pagination.
2. The idea still haunted Boole when he wrote An Investigation of the Laws of Thought, on which are founded the Mathematical Theories of Logic and Probabilities, Walton and Maberley, London 1854 (referred to hereafter as LT). There, in a footnote (LT 406), he recognizes the possibility of sciences erected on fundamental ideas which ‘might be wholly different from those with which we are at present acquainted’.
3. ‘On the Theory of Probabilities, and in particular on Mitchell’s Problem of the Distribution of Fixed Stars’, The Philosophical Magazine, Series 4, vol. i, 1851, pp. 521–30. Reprinted in CLW, pp. 247–59. The quotation is on p. 252 of the reprint.
4. At LT 50 Boole takes up the theme of the possibility of other logics and stresses the hypothetical character of this train of thought. It does not imply, he points out, that our logic ‘is the product either of chance or of arbitrary will. This remark is also true, by the way, if logic is considered as part of our culture.
5. Taylor and Walton, London 1851 (referred to hereafter as CoS). Reprinted in CLW, pp. 187–210; references are to the pagination of the reprint.