of natural science. This logic also influenced Husserl’s teacher, Brentano. Even Husserl himself learned a good deal, both positively and negatively, from Mill.
2. Christoph Sigwart, Logik, 2 volumes, 1873ff.22 A vast and important work on logic, recently published in its fifth edition edited by Hans Meier.
In the traditional fashion, the first volume treats the theory of judgment, concept, and conclusion. The second volume treats the theory of method. Sigwart takes it upon himself to bring logic into close connection with the project of the sciences. In the second volume he specifically pursues an orientation to the philosophy of science. This logic has had its greatest influence on one of the contemporary schools of philosophy: the so-called value philosophy of Windelband and Rickert.
3. Hermann Lotze’s Logic, published in 1874 as part 1 of his System of Philosophy. 23 It is equally as important as, and maybe even more es-sential and relevant than, Sigwart.
It is in three books: “Of Thought,” “Of Investigation,” and “Of Knowledge.” Philosophically speaking, the most important book is the third. It has exercised a strong influence on the modern logic that is usually called the logic of [28] validity, or validity logic, or value logic. It has had an influence on Windelband and Rickert, but likewise, in some essential elements, on Husserl. That is especially so as regards the peculiar interpretation of the Platonic idea in book 3 of the Logic, where Lotze tries to show that the Platonic idea is not a sensory thing but rather (to use his term) “has validity.” Already in 1843, when he was a young teacher, he had written a logic that was a livelier and, in my opinion, a philosophically more acute work.24 The large logic has recently been re-edited by Georg Misch
22. [Christoph Sigwart (1830–1904), Logik (Tübingen: H. Laupp, 1873–1878; 5th edition, 1924, ed. Hans Meier). See also Christoph Sigwart, Logic, 2nd rev. edition, 2 vols., trans. Helen Dendy (London: Swan Sonnenschein / New York: Macmillan, 1895); repr. in the series Phenomenology: Background, Foreground, and Influences (no. 12), 2 vols. (New York and London: Garland Publishing, 1980).]
23. [Hermann Lotze (1817–1881), Logik. Drei Bücher vom Denken, vom Untersuchen und vom Erkennen: System der Philosophie (Leipzig: S. Hirzel, 1874; 2nd edition, 1880), vol. 1. See also Hermann Lotze, System of Philosophy, Part I. Logic, in Three Books: Of Thought, Of Investigation, and Of Knowledge, 2 vols., ed. and trans. Bernard Bosanquet (Oxford: Clarendon Press, 1884). The second edition (1888) was reissued in the series Phenomenology: Background, Foreground, and Influences (no. 8), 2 vols. (New York and London: Garland Publishing, 1980).]
24. [Heidegger is referring to Lotze’s Logic (Leipzig: Weidemann, 1843).]