in question, then the laws have to be taken from thinking itself. And not from just any kind of constructed thought, but from the actual acts and procedures of thought. In other words, the laws are to be sought in the living activity of the very processes of thought. Active thinking is the same as the mental occurrence, the mental reality, that must produce the laws. But mental reality is the theme of psychology. Therefore, [38] the basic project of logic—which is to get the laws of thought and to characterize the very act of thinking (which still remains a mental process)—belongs within the competence of psychology. So psychology is logic’s foundational discipline.
Thus John Stuart Mill writes:
[Logic] is not a Science distinct from, and coordinate with, Psychology. So far as it is a science at all, it is a part, or branch, of Psychology; differing from it, on the one hand as a part differs from the whole, and on the other, as an Art differs from a Science.2 Its theoretic grounds are wholly borrowed from Psychology, and include as much of that science as is required to jus-tify the rules of the art. (John Stuart Mill, An Examination of S. W. Hamil-ton’s Philosophy.3 Compare Husserl, Logical Investigations, vol. 1, “Prolegom-ena to Pure Logic,” chap. 5, pp. 78 ff.)4
And Theodor Lipps:
The very fact that logic is a special discipline within psychology distin-guishes each from the other in a sufficiently clear way. (Grundzüge der Logik, 1893, §3)5
Compare further:
2.[Heidegger glosses: “That is, as a Kunstlehre or technique [differs] from a theoretical reflection.”]
3. [Heidegger cites the German as it appears in the first edition of Husserl’s Logische Untersuchungen, vol. 1, §17, p. 51 / tr. 90–91. Mill’s text is from John Stuart Mill, An Examination of Sir William Hamilton’s Philosophy and of the Principal Philosophical Questions Discussed in his Writings, 5th edition (London: Longmans, Green & Co., 1878), p. 461: Heidegger cites the text in Theodor Gomperz’s translation. The work is reprinted as vol. 9 of John Stuart Mill, Collected Writings, 33 vols., ed. John M. Robson (Toronto: University of Toronto Press / London: Routledge & Kegan Paul, 1981–1991); here, vol. 9, p. 359.]
4. [In LU, vol. 1, §§25–26, pp. 78–84 / tr. 111–115, Husserl discusses Mill’s position on the law of contradiction. Neither Weiss nor Moser provides this reference, which means that Heidegger did not read it out in class.]
5. [Theodor Lipps (1851–1914), Grundzüge der Logik (Hamburg and Leipzig: J. A. Barth, 1893; 2nd edition, 1911). Heidegger takes the citation from Husserl, LU, vol. 1, §18, p. 52 / tr. 91.]