1 Notable recent works include Bonjour, Lawrence In Defense of Pure Reason (Cambridge: Cambridge University Press 1998);Google Scholar Casullo, Albert A Priori Justification (Oxford: Oxford University Press 2003);CrossRefGoogle Scholar Hanson, Philip and Hunter, Bruce eds., Return of the a priori (Canadian Journal of Philosophy, supplementary volume 18 [1992]);Google Scholar Boghossian, Paul and Peacocke, Christopher eds., New essays on the a priori (Oxford: Clarendon Press 2000).CrossRefGoogle Scholar

2 See n. 19 below.

3 The reason for the caginess — that Ockham apparently deserves credit for the canonical account of the distinction—is that the earliest history of the a priori remains murky. Ockham is the earliest philosopher known to me to have given the terms their canonical medieval definitions, yet it is possible that he was merely repeating what had already been written by a predecessor. One certain point is that while Ockham may be given credit for having defined ‘a priori’ and ‘a posteriori,’ he cannot be seen as having coined the terms or invented an entirely new topic. Instead, he defined them while working on traditional texts and topics. The central text is the Aristotle's Posterior Analytics, 1.2. Although they did not explicitly define what they meant by ‘a priori’ and ‘a posteriori,’ Aquinas and Buridan (among others) did use the words and were critical in establishing the topic with which Ockham was engaged. For Aquinas, see, e.g., In Phys II. 15.5 and In Post An 1.42.3; for Buridan, see, e.g., Summulae de dialectica VIII, 8, 1 (where the same example discussed by Ockham appears). Some discussion of the issues can be found in Stump, Eleonore 'Aquinas on the Foundations of Knowledge,’ in Aristotle and His Medieval Interpreters, Bosley, Richard and Tweedale, Martin eds. (Canadian Journal of Philosophy, supplementary volume 17 [1991]), esp. 154f.Google Scholar

4 Summa Logicae, III-2, cap.17 (all translations of Ockham are my own).

5 This summary of Ockham's Statements on the a priori is indebted to Moody, Ernest A. The Logic of William of Ockham (New York: Sheed & Ward 1935), 252–80.Google Scholar

6 For example, although this search was not exhaustive, neither ‘a priori’ nor ‘a posteriori’ were found in Bacon, Galileo or Suarez.

7 Commentarii in libros duos Posteriorum Analyticorum, bound in Zabarella's posthumous Opera Logica (Cologne, 1597), 691e-f (Zabarella translations are mine).

8 For example, see 664f.: when we consider things ‘without qualification and in accordance with their own natures, the causes are prior to their effects, because nature generates effects from causes….’ For another example, see the passage from his In libros Aristotelis Physicorum commentarii discussed by Gilbert, Neal W. Renaissance Concepts of Method (New York: Columbia University Press 1960), Ch. 7.CrossRefGoogle Scholar

9 Summa philosophica quadripartita, I, 224 (my translation).

10 Although the foregoing discussion has focused on Ockham (and his successors), this is not because he was the most important source of medieval philosophy for Descartes or Spinoza. Instead, the focus is on Ockham for conceptual reasons: namely, because he (apparently) was the philosopher who formalized the words, making them terms of art for philosophical discourse. While Descartes was widely read in the medievals (see Gilson's study, cited in the next note, for convincing evidence of this), Spinoza usually relied on more contemporary texts when he employed scholastic terminology and concepts. His two most important sources are the Institutionum metaphysicarum libri duo by Franco Burgersdijck (London, 1653) and the Disputationes ex philosophia selectae by Adriaan Heereboord (Leiden, 1650). Both books were in his library (see Catalogus van de biblioteek der Vereniging ‘het Spinozahuis’ te Rijnsburg, Alter, J.M.M. ed. [Leiden: E.J. Brill 1965]Google Scholar) and both contain the two main senses of the a priori that this paper finds in Spinoza.

11 Gilson records some seventeen appearances of ‘a priori’ in Descartes’ corpus; see the entry under ‘démonstration’ in his Index Scolastico-Cartésien (repr. New York: Burt Franklin, no date), 66.

12 For the most important exception, see the next section.

13 This and all translations of Descartes are from the respective volume of The Philosophical Writings of Descartes, vols. I-III, trans. John Cottingham, Robert Stoothoff and Dugald Murdoch (with Anthony Kenny contributing to vol. III) (Cambridge: Cambridge University Press 1984-1991). References to this translation will be ‘CSM' ('CSMK’ for vol. III) plus the volume and page numbers, along with Adam and Tannery references. The quotation from the letter to Mersenne is CSMK III: 38 (A-T I: 250-1).

14 Here is as good a place as any to acknowledge a certain looseness in this paper's discussion. Sometimes it will be speaking about a priori demonstrations; at others, about a priori knowledge or a priori justification. There are no doubt important differences in the a priority of demonstration versus knowledge versus justification. While these differences would have to be reckoned with in a different sort of paper, they don't pose a problem for this one. That's in part because of the scope of this paper (which Covers the macro-history of the a priori, in all its forms), in part because of the looseness in how Spinoza himself used and conceived of the a priori. Our sharp distinctions between demonstration, knowledge and justification were not made by him; it would be anachronistic to try to read them into him.

15 Whereas Descartes often used ‘a priori’ and ‘a posteriori,’ Spinoza apparently employed them only f our times: Descartes’ Principles of Philosophy Part I, Prop. 6; Cogitata Metaphysica Part II, Ch. I; Ethics IPllSch; Letter 83. One explanation for why Spinoza used them relatively infrequently is that in his day, they still had their medieval causal connotation, a connotation in which he was for the most part uninterested. As stated below (n. 19), it was only with Leibniz that the medieval connotation was finally lost and a new one arose (though not the same one Spinoza would have wanted). (NB: The Standard abbreviations will be used when referring to the Ethics: a Roman numeral for ‘Part,’ ‘D’ plus an Arabic numeral for ‘Definition,’ ‘P’ plus an Arabic numeral for ‘Proposition,’ ‘Sch’ (plus an Arabic numeral where appropriate) for ‘Scholium,’ ‘Pref for ‘Preface,’ ‘App’ for ‘Appendix,’ etc.)

16 Part II, Ch. 1. Translation by Curley, Edwin in The Collected Works of Spinoza, vol. 1 (Princeton: Princeton University Press 1985), 316Google Scholar (G1:250). Unless otherwise stated, this and all Spinoza translations will be Curley's (with occasional changes). In-text citations will be provided to Spinoza's texts and, where it is required to fix precisely the reference, Gebhardt's critical edition (abbreviation: ‘G’ plus the volume and page number).

17 Translation by Samuel Shirley in Spinoza: The Letters (Indianapolis: Hackett Publishing 1997).

18 Moody, William of Ockham, 251.Google Scholar While Moody's felicitous phrase nicely evokes the character of a priori knowledge for Ockham — it is both factual and rational — he infelicitously diminished the force of his argument by subsequently calling a priori demonstrative knowledge ‘analytic in character’ (258). The whole point is that for Ockham, we can possess knowledge that is both a priori and non-analytic in character, because we can possess knowledge that is both a priori and factual. See the next note for speculation on the actual origins of the type of knowledge that Moody wrongly attributed to Ockham.

19 We can ask — when did a priori knowledge come to be knowledge acquired independently of experience? The credit for this development is usually given to Hume, who distinguished between matters-of-fact and relations-of-ideas and insisted that relations-of-ideas alone can be known a priori. Robert Merrihew Adams, however, has recently argued that the innovation was due to Leibniz (Leibniz: Determinist, Theist, Idealist (Oxford: Oxford University Press 1994), esp. 109-10). In my opinion, Adams is right to attribute to Leibniz ‘a crucial role in the transformation of the meaning of “a priori'” (110), though he doesn't portray this role quite correctly. Whereas Adams just sees Leibniz as changing the meaning of an a priori demonstration, he actually accomplished much more: he also was instrumental in creating a whole new category of knowledge that may be called ‘a priori.’ For evidence of this claim, see, e.g., §13 of the Discourse on Metaphysics and the 1686-87 correspondence with Arnauld.

20 Mancosu, Paolo has shown that the causality of geometry was subject to debate in the early modern period (Philosophy of Mathematics and Mathematical Practice in the Seventeenth Century (Oxford: Oxford University Press 1996), esp. Ch. 1).Google Scholar Though it is not possible here to defend fully the assumption that Descartes did not take geometrical relations to be causal relations, some remarks are needed to render it at least plausible. Let me make two points. First, Descartes’ views on causation were heavily influenced by the new mechanistic science, which in turn heavily favors the efficient over the other three traditional causes. Because it is very hard to see how the efficient cause can enter into the production of geometrical entities (as Mancosu argues, even those who conceived of geometry as causal did so in terms of the formal and material causes, not the efficient or final), it is very hard to see how geometrical relations could be causal for Descartes. The second point is textual. In his Géometrie, Descartes rarely or never described geometrical relations in causal terms. Conversely, in the chief texts where he talked about causation (such as the so-called causal principle of the Third Meditation [CSM II: 28; A-T VII: 40] and his most general Statement of a cause in the Fourth Replies [CSM II: 166; A-T VII: 238]), he never employed geometrical language. This is empirical evidence supporting the inductive inference that causation and geometry were separated in Descartes' thought. For more texts as well as valuable critical discussion of Descartes’ broader theory of causation (including arguments that he had a theory), see Clatterbaugh, Kenneth The Causation Debate in Modern Philosophy, 1637-1739 (New York and London: Routledge 1999), esp. Ch. 2.Google Scholar

21 Much has been written on this passage. Among the more helpful commentaries are Doney, Willis ‘The Geometrical Presentation of Descartes's A Priori Proof,’ in Descartes: Critical and Interpretive Essays, Hooker, Michael ed. (Baltimore: Johns Hopkins University Press 1978),Google Scholar and Curley, Edwin ‘Analysis in the Meditations: The Quest for Clear and Distinct Ideas,’ in Essays on Descartes’ Meditations. Amélie Oksenberg Rorty, ed. (Berkeley and Los Angeles: University of California Press 1986).Google Scholar

22 Whether Descartes used the synthetic method in some of his other works (especially the Principia) is a matter of scholarly dispute. For texts and discussion, see Curley, 'Analysis in the Meditations,’ 155 and 172 n.7.

23 As Curley writes, ‘though Descartes no doubt understands [a priori and a posteriori in the traditional causal way]…, it is hard to see that the Meditations exemplify a procedure that is, in that sense, a priori. The Meditations begin, on the face of it, with a proof of the existence of the self, proceed to proofs of the existence of God, and then move on to a proof of the existence of the world, that is, they go from effect to cause and back again to effect’ ('Analysis in the Meditations,’ 155).

24 Cf. Doney, ‘Descartes's A Priori Proof,’ 13f., and Curley, ‘Analysis in the Meditations, ' 153.Google Scholar

25 A constant between pre-and post-Cartesian philosophy was the valuation by many philosophers of a priori demonstration as the superior kind of demonstration; what changed was the conception of this kind of demonstration.

26 As we have seen, his followers like Spinoza continued to use the words ‘a priori’ and 'a posteriori’ in the traditional causal sense. The causal sense is also the official one defined by Arnauld and Nicole in the Port-Royal Logic, IV.1, published in 1674. It is not surprising that the official meaning should linger even after philosophy had moved on: there is often a lag between the occurrence of conceptual developments and their appearance in language.

27 While no explanation was provided in this section for the transition from the causal to the epistemic a priori that occurred in the early modern period, it should not be inferred that the change was arbitrary. To the contrary: a number of possible reasons suggest themselves, including one having to do with changing theories of perception. According to Standard scholastic and Aristotelian accounts of perception, the data of experience represent the world by resembling it. The resemblance requirement was set aside in the early modern period, which favored mechanistic views where our experiences are produced by unknown causes that have nothing to do with the appearance of the effects. Because of this view on the origins of experience, the early moderns would have held that any argument based on experience would be a posteriori, since the perceptual data are effects of hidden causes. For more, see Gueroult, Martial Etudes sur Descartes, Spinoza, Malebranche et Leibniz (New York: Georg Olms Verlag Hildesheim 1970), 16f.Google Scholar

28 For an excellent discussion of the difficulties involved in rendering this phrase in English, see Gabbey, Alan ‘Spinoza's Natural Science and Methodology,’ in The Cambridge Companion to Spinoza, Garrett, Don ed. (Cambridge: Cambridge University Press 1996), 170–5.Google Scholar

29 See note 27 for one reason why the data of opinion and imagination are ultimately incomprehensible.

30 How good an example it is has been the subject of discussion, with some scholars arguing that it offers at best an analogy, what the different kinds of knowledge are like, and not an exact illustration of what they really are (see, e.g., Curley, E.M. 'Experience in Spinoza's Theory of Knowledge,’ in Spinoza: A Collection of Critical Essays, Grene, Marjorie ed. [Garden City, NY: Anchor Books 1973]Google Scholar). Since the interpretative Claims of this paper don't require it to be either a literal or a figurative illustration of the three kinds of knowledge, it doesn't matter to the present argument which way it is to be taken.

31 Some commentators have linked Spinoza's common notions to the Stoics’ common notions or ennoia (see, e.g., Gueroult, Martial Spinoza II—L'âme [Paris: Aubier-Montaigne 1974]Google Scholar, Appendix 12). This can't be right. For one reason, the Stoics’ ennoia emerge from sensory experience whereas Spinoza's common notions are innate. In addition, ennoia serve as criteria for truth; not so for Spinoza. So the Stoics and Spinoza clash over such basic matters as the Status of common notions in our cognitive constitutions and their contribution to the justification of our knowledge. A better Interpretation of common notions in Spinoza will be offered below.

32 For others who have interpreted common notions as being in some sense laws of nature, see Wolfson, H.A. The Philosophy of Spinoza, vol. 2 (Cambridge, MA: Harvard University Press 1934), 162;Google Scholar Parkinson, G.H.R. Spinoza's Theory of Knowledge (Oxford: Clarendon Press 1954), 164;Google Scholar and Wilson, Margaret D. ‘Spinoza's Theory of Knowledge,' in Cambridge Companion, Garrett, ed., 113fGoogle Scholar

33 Spinoza's views on laws of nature remain understudied. Although it has been validly criticized in a number of ways, the most important general study is still Curley, E.M. Spinoza's Metaphysics: An Essay in Interpretation (Cambridge, MA: Harvard University Press 1969).CrossRefGoogle Scholar For an introduction to the relevance of the laws to his epistemology, see Wilson, ‘Spinoza's Theory of Knowledge.’ A more recent study is Jon Miller, ‘Spinoza and the Concept of a Law of Nature’ (History of Philosophy Quarterly 20 [2003]).Google Scholar

34 As Spinoza said in the chapter on law in the Political-Theological Treatise (TTP), ‘a universal law governing all bodies’ allows us to know that ‘all bodies colliding with smaller bodies lose as much of their own motion as they impart to other bodies,’ and a law that ‘necessarily follows from the nature of man’ predicts that ‘a man, in remembering one thing, forthwith calls to mind another like it, or which he has seen along with it’ (TTP Four [G III: 57-8]; this and all translations of the TTP are by Samuel Shirley [Indianapolis: Hackett Publishing 1998]). As to causality, see his official definition of a law, also in the TTP: ‘The word law, taken in its absolute sense, means that according to which each individual thing … [acts] in one and the same fixed and determinate manner’ (TTP Four [G III: 57]).

35 Cf. TTP Seven: ‘Now in examining natural phenomena we first of all try to discover those features that are most universal and common to the whole of Nature, to wit, motion-and-rest and the laws and rules governing them which Nature always observes and through which she constantly acts; and then we advance gradually from these to other less universal features’ (G III: 102).

36 For a couple of texts where Spinoza endorsed the notion that a modal or intensional property of the premises of an argument is transferred to any conclusion drawn from those premises, see the preface to his commentary on Descartes’ Principles of Philosophy and IIP40. For discussion, see Mason, Richard ‘Concrete Logic,’ in Spinoza: Metaphysical Themes, Koistinen, Olli and Biro, John eds. (Oxford: Oxford University Press 2002).Google Scholar

37 Critique of Pure Reason, B3; trans. Kemp-Smith, Norman (New York: St. Martin's Press 1965), 43Google Scholar

38 See, e.g., In Defense of Pure Reason, 102.

39 Boghossian, Paul and Peacocke, Christopher ‘Introduction,’ in Boghossian and Peacocke, New Essays, 3Google Scholar

40 In Defense of Pure Reason, 102

41 In Defense of Pure Reason, 101

42 This takes Bonjour to be denying that one directly intuits the relation of exclusion between the particular ideas ‘red’ and ‘green’ without recourse to a more general rule of which this particular antipathy is a specific case. If this is not the correct reading of Bonjour but instead he should be understood to hold that the inference is direct, then he couldn't be an ally of Spinoza's at this juncture. The possible ambiguities of Bonjour's views on whether the a priori involves general rules will be critically evaluated in the final section below.

43 Lest one object that Spinoza's view is too bizarre to be taken seriously, it may be pointed out that he is not the only one to have held it; at least since the ancient Stoics, philosophers have also argued for a Substantive conception of reason according to which the rational person must not only be able to draw correct inferences but also must know a certain minimal number of truths or propositions. For discussion of the philosophical issues, see Føllesdal, Dagfinn ‘The Status of Rationality Assumptions in Interpretation and in the Explanation of Action,’ reprinted in Readings in the Philosophy of Social Science, Martin, Michael and McIntyre, Lee C. eds. (Cambridge, MA: MIT Press 1994), esp. 300f.Google Scholar, and Brandom, Robert B. Tales of the Mighty Dead (Cambridge, MA: Harvard University Press 2002), 1–17.Google Scholar

44 For other important texts on the innate activity of ideas, see IIP43S, P48S and P49S2.

45 Corresponding to Spinoza's views on the interconnectedness of ideas are his views on the interconnectedness of bodies. For discussion of the interconnectedness of bodies and its relationship to the interconnectedness of ideas, see Lloyd, Genevieve Part of Nature: Self-Knowledge in Spinoza's Ethics (Ithaca: Cornell University Press 1994), 10f.CrossRefGoogle Scholar

46 ‘The Programme of Moderate Rationalism,’ in Boghossian and Peacocke, New Essays, 260

47 This conception of justification also bears some resemblance to one discussed by Descartes in the Regulae. In rule four of the Regulae, Descartes distinguished between two ‘modes of knowing,’ deduction and intuition (CSM1:15; A-T X: 369). The chief difference between deduction and intuition is that the former justifies conclusions on the basis of distant premises which ‘we cannot take in at one glance’ whereas intuition draws its inferences solely from immediately adjacent ‘single propositions' (CSM I: 15, 14; A-T X: 369-70). There are undoubtedly affinities between what Descartes said here and Spinoza; just as Spinoza held of reason and intuition, Descartes said that deduction and intuition are the two ‘most certain routes to knowledge that we have’ (CSM I: 15; A-T X: 370). Yet the affinities should not be pressed too far. For one thing, the Regulae was published after Spinoza died, so it is unlikely that he read and was influenced by it. More importantly, there are major conceptual differences between Descartes and Spinoza. For example, while Descartes argued that intuition can justify only self-evident truths and deduction only the non-self-evident, according to Spinoza, both ways of Coming to know can justify either self-evident or non-self-evident truths.

48 Barbone, Steven ‘What Counts as an Individual for Spinoza?’ in Koistinen and Biro, Spinoza: Metaphysical Themes, 99Google Scholar

49 This Interpretation was first suggested by Mason, Richard ‘Spinoza on Modality,’ The Philosophical Quarterly 35 (1986).Google Scholar It was fully developed and defended by Miller, Jon ‘Spinoza's possibilities,’ The Review of Metaphysics 54 (2001).Google Scholar

50 In a well-known letter (Ep. 32), Spinoza discussed how a change in perspective could affect the assessment of an event's modal Status. To use the example he provided in that letter, an event may be necessary from the perspective of a ‘worm in the blood’ but not from the perspective of the human whose blood the worm is in. Because of the susceptibility of modality to perspective, one cannot assert absolutely that an event is necessary since a change in perspective (say, switching from the worm's perspective to the human's) could entail a change in necessity. For an elaboration of this relativistic interpretation of Spinoza's modal views, see Curley, Spinoza's Metaphysics, 115f.Google Scholar

51 For further discussion of whether intuitive knowledge is inferential, see Gueroult, Spinoza, 447f,Google Scholar together with Wilson, ‘Spinoza's Theory of Knowledge,’ 118f.

52 While most of ‘God's revelations were received only with the aid of the imaginative Faculty,’ Spinoza said that ‘God's ordinances leading men to salvation were revealed not by words or by visions, but directly [to Christ]….’ (TTP One [G III: 21]). The knowledge that Christ gained as a result of his communication with God is plainly not an instance of vaga experientia, for it is in precisely this respect that Christ differed from other prophets. Moreover, it doesn't seem to be an instance of rational knowledge, for Spinoza said that when Christ formed his knowledge of God, he perceived ‘by pure intuition that which is not contained in the basic principles of our cognition and cannot be deduced therefrom’ (ibid.). On the assumption that the 'basic principles of our cognition’ alluded to are the ‘common notions’ discussed in the Ethics, Christ's knowledge was formed without reliance on the general rules or laws that are constitutive of common notions and hence rational knowledge.

53 In the past, the value of Spinoza's so-called ‘political’ works for understanding his 'metaphysical’ and ‘epistemological’ writings has been doubted (see, e.g., Bennett, Jonathan A Study of Spinoza's Ethics [Indianapolis: Hackett Publishing 1984], 7Google Scholar). This paper assumes that such doubts have been put to rest by, among others, Edwin Curley, ‘Notes on a Neglected Masterpiece (II): The Theological-Political Treatise as a Prolegomenon to the Ethics,’ in Central Themes in Early Modern philosophy, Cover, J.A. and Kulstad, Mark eds. (Indianapolis: Hackett Publishing 1990).Google Scholar

54 Peacocke, ‘The Programme of Moderate Rationalism,’ 263Google Scholar

55 The discussion of Christ here is necessarily truncated, designed only to reinforce previous conclusions and not to introduce new premises into the argument. For a much more extensive and detailed analysis of the so-called ‘Christ question,’ see Matheron, Alexandre Le Christ et le salut des ignorants chez Spinoza (Paris: Aubier-Montaigne 1971).Google Scholar

56 Ian Hacking argued several decades ago that Descartes had a fundamentally different conception of proof from ours. More recently, David Owen has contended that early modern conceptions of reason are incommensurate with post-Fregeian conceptions. For more, see: ‘Leibniz and Descartes: Proof and Eternal Truths,’ reprinted in Hacking, Ian Historical Ontology (Cambridge, MA: Harvard University Press 2002);CrossRefGoogle Scholar Owen, David Hume's Reason (Oxford: Oxford University Press 1999), esp. Chs. 1–3.Google Scholar

57 Among the many interesting questions are who coined ‘a priori’ and to what end (see n. 3 above), why the usage of ‘a priori’ expanded considerably in the first decades of the 1600s, how exactly Leibniz contributed to the evolution in the meaning of ‘a priori’ (n. 19), and how Leibniz's contributions differ from Hume's.

58 Being Spinozistic, these criticisms are meant to be friendly, offered by a rationalist who is pleased that his fellow rationalists are defending the a priori but who thinks there are problems with their arguments. For a different kind of criticism, presented by someone who is outside the rationalist tradition, see Aune, Bruce A. ‘Against Moderate Rationalism,’ Journal of Philosophical Research 27 (2002).CrossRefGoogle Scholar

59 See ‘The Programme of Moderate Rationalism,’ 256, 275, 283, etc.

60 To be fair to Peacocke, he may be using ‘rational’ here as a synonym for ‘intelligible' or ‘explicable,’ intending to contrast rational with non-rational intuition. If that's the case, however, he unfairly disparages Spinoza when he says that ‘the phrase “rational intuition” has historically been associated with some of the headier forms of rationalism’ (257-8). Spinoza (and probably other historical rationalists) can claim to have provided an account of the nature of intuition and so not to have invoked a mysterious power of the sort that worries Peacocke.

61 In Defense of Pure Reason, 102

62 Ibid., 15

63 The seeds for this paper were planted in a seminar on the a priori held at NYU in winter 2001; my thanks to Paul Boghossian and Christopher Peacocke for an invigorating classroom experience. Early versions were presented at Queen's University in November 2002 and Carleton College in February 2003; thanks to all present — especially Lilli Alanen, E.J. Bond and Gary Iseminger — for the stimulating discussions. I am also gratef ul to John Carriero, Brad Inwood, Henrik Lagerlund, Calvin Normore and Robert Pasnau for valuable conversations and correspondence on various points concerning the early history of the a priori. Finally, I wish to give Special thanks to Phillip Mitsis, Catherine Wilson, two anonymous referees, and an anonymous editor of this Journal for their extensive and extremely useful written comments.