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Essences and Discovery: Plato, Locke, and Leibniz

  • Douglas Odegard (a1)


According to Plato's Republic, human knowledge in highest form owes its existence to a priori discoveries made during the course of dialectical investigations. Being a priori, such discoveries are neither empirical observations nor conclusions based upon empirical observations, although in some cases they may be “occasioned” by experience. They are matter for intellectual, not literal, vision, and making them is what distinguishes the successful philosopher from the non-philosopher. Thus, in the Phaedo, Plato is in a position to argue that the separation of the soul from the body in death is no evil for a genuine philosopher: he has no need to rely on the bodily senses in order to acquire philosophical knowledge; and he is well free of the errors and confusion generated by the senses, and of the physical desires nourished in the soul as a result of residing in a body.



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1 More precisely, to recollections occurring in dialectical inquiries. Because it has no substantial bearing on the aims of this paper, I shall make very little future reference to the doctrine that human knowledge is recollection.

2 i.e., An Essay Concerning Human Understanding, Book III, chapter iii, section 12 References are made to A. C. Fraser’s two-volume edition, Oxford, 1894.

3 Remembering that for Locke essences are of sorts of things and not of individuals. See E III vi 4–6.

4 This is a view which Locke does seem to hold, although it runs into some difficulty over the possibility of distinguishing words which signify the abstract idea of justice from words which merely correctly apply to any case of justice, such that not all the latter words are necessarily the former.

5 “Nominalistic” in the indicated sense, and not in any sense in which a nominalist rejects abstract ideas altogether.

6 As distinct from [a] “the abstract idea signified by any word which signifies the abstract idea of justice,” and [b] “the abstract idea which the word ‘justice’ now, as a matter of fact, signifies.” Obviously, there are difficulties here as well.

7 “Seems” because, in one version of the position he is suggesting, a definition must still have the form “The word ‘x’ means x” and is therefore still apparently subject to the charge of vacuousness [although of a logically, different kind]. The point is incidental to this discussion, however, because [a] arguments available to remove the vacuousness of Platonic definitions can also be effective in removing this type of vacuousness, and [b] a serious advocate of this kind of definition, as opposed to Platonic definitions, could consistently introduce changes to meet the charge—e.g., he might maintain that “The word ‘x’ means y” itself amounts to ‘‘The words ‘x’ and ‘y’ mean the same thing,” and work on from there.

8 For his attack on certain of these claims, see E III vi. For his rejection of universals beyond abstract ideas and general words, see E III iii passim.

9 Using “non-identical” to exclude both identicals proper and semi-identicals, where the area of discourse is confined to categorical truths.

10 i.e., New Essays Concerning Human Understanding, trans. A. G. Langley, La Salle, 1949. Book III, chapter vi, section 10.

11 i.e., in a sense which makes no demands on the structure of the sentences used to express the propositions.

12 From “Reflections on Knowledge, Truth, and Ideas” in Leibniz Selections, ed. P. P. Wiener, New York, 1951. Originally published in Acta Eruditorum, 1684. See also NE II xxix 2, 4; NE II xxxi 1, 2; Discourse on Metaphysics, xxiv.

13 Curiously enough, Leibniz calls such a definition a “nominal definition” as long as it fails to reach the point where it reveals a priori the possibility of the thing defined.

Essences and Discovery: Plato, Locke, and Leibniz

  • Douglas Odegard (a1)


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