• Frege, G. (1892) "On Sense and Reference", originally published as " Über Sinn und Bedeutung" in
Zeitschrift für Philosophie und philosophische Kritik, vol. 100, pp. 25–50. Transl. Geach & Black 56–78. • Mill, J. S.,
A System of Logic, London 1908 (8th edition). •
Peter of Spain Summulae Logicales, ed. I. M. Bochenski (Turin, 1947) – also quoted in Prior 1976. • Prior, A. N.
The Doctrine of Propositions & Terms, London 1976. • Strawson, P. F. "On Referring",
Mind 1950 pp. 320–44. • William of Ockham,
Summa logicae, Paris 1448, Bologna 1498, Venice 1508, Oxford 1675.