A central part of Omri Boehm's book, Kant's Critique of Spinoza (especially Chapters 2&3) is a re-reading of Kant's antinomies in order to show that these address Spinoza and Spinozism in order to help explain the Critical Kant's claim that the two viable metaphysical options are either Kant's Transendental Idealism, which in Boehm's hands is itself a regulative Spinozism, or a Transcendental Realism, which can be best understood as a species of metaphysical Spinozism (recall this post; and also this post on the debate over the PSR between Garber and Della Rocca as well Alex Douglas's post). I am fully persuaded by Boehm that Spinoza is, indeed, a central interlocutor (for the bad reason that it fits my views of the pre-Critical Kant).
Boehm notes correctly that Descartes and Leibniz, who distinguished between space as indeterminately large and as infinitely large in order to claim that space was indeterminately large (not infinite), reserved "true infinity to God." (75) By contrast, "Spinozism is committed to the world's infinity." (79) This suggests to Boehm (and I agree) that Kant is concerned with Spinozism in the first antinomy's anthithesis. But does it follow that Spinoza is the only such Spinozist known to Kant? I think not. For, Newton, too, is such a Spinozist not just in texts unknown to eighteenth century readers, but also in the General Scholium (and the Principia more generally). This is not obvious if one identifies, as too many Kant scholars stilll do, Clarke's correspondence with Leibniz as the Newtonian position. Even if there weren't Newtonian texts (known to Kant) that suggest otherwise, it would be a mistake to treat Clarke's presentation as echt-Newton because the whole exchange between Leibniz and Clarke is framed from the start by Leibniz's insinuation at the start of the exchange that Newton is a crypto-Spinozist (an explosive charge by the time Leibniz makes it).
For, Newton embraced the true infinity of space right at the start of the Principia: ‘‘Now no other places are immovable but those that, from infinity to infinity [ab infinito in infinitum], do all retain the same given position one to another, and upon this account must ever remain unmoved and do thereby constitute immovable space,’’ (Principia, scholium to the definitions). This is is a core Newtonian commitment unchanged through all the editions (see here for more details). In the General Scholium, added to the Principia's second edition, Newton explains the relationship between God and infinite space. I quote two passages:
[A] [God] endures always and is present everywhere, and by existing always and everywhere he constitutes duration and space. Since each and every particle of space is always, and each and every indivisible moment of duration is everywhere, certainly the maker and lord of all things will not be never and nowhere (quoted from the Cohen/Whitman translation, p. 941).
[B] “the supreme God necessarily exists, and by the same necessity he is always and everywhere” (941; emphases added)
On [A] God and time (and space) co-exist eternally – so there is no first creation of a moment of time. While Newton denies that God should be identified with space (and time), "He is not eternity and infinity, but eternal and infinite; he is not duration and space, but he endures and is present," God is, thus, always and everywhere immanent within the order of nature (understood as existing in space and time). Newton does not shrink back from claiming that space and time are truly infinite. Moreover, space's existence is a (non-causal) consequence of God's existence ("by existing always and everywhere he constitutes duration and space"). In the General Scholium, Newton does not explain the nature of this consequence. (There is a rich scholarly literature on Newton's (ms) De Grav, where Newton both recognizes the infinite/indefinite distinction which he associates with Descartes's fears about being acccused of atheism, and offers an emanative account of the relationship between God and space; see here for my treatment and survey of literature.)
In the fourth letter to Bentley (which became public in the middle of the eighteenth century), Newton allows “there might be other systems of worlds before the present ones, and others before those, and so on to all past eternity, and by consequence that gravity may be coeternal to matter, and have the same effect from all eternity as at present” (in the Janiak translation, 102). The pre-Critical Kant also embraced the position that ‘‘infinite space teems with cosmic systems’’ [der unendliche Weltraum von Weltgebäuden wimmele] (UNH, Part 1, chapter 1 257 (247)). In context, Kant refers to Huygens (who is, in part, responding to Newton) as his source.
On [B] the modal status of God’s existence and God’s infinite spatiality is said to be identical. So if God is, infinite space (and time) is. Newton does not explain his views on necessity in the General Scholium (or elsewhere, I think), but I pointed out last week that now-less-familiar works by Clarke do so in terms of the final halting point of the PSR. Either way, Newton's views on God, space, and time are Spinozist. (Obviously in this post I have not said anything to motivate the thought that Newton is a monist about substance; but see here.)
Of course, Newton's views are not identical to Spinoza because Newton treats space and time relatively symmetrically whereas in Spinoza space is and time is not an attribute of substance. In fact, it is worth noting that Kant (in a passage frequently quoted by Boehm) treats Spinozism as the view, "in which space and time are essential determinations of the original being itself." (Critique of Practical Reason) As such this characterization is closer to the historical Newton than to the historical Spinoza. (Boehm recognizes, of course, that Kant treats space and time more symmetrically than Spinoza does.)
So, returning to Boehm, he is simply wrong when he identifies Newton with the view "that the world is not infinite and has a beginning" (80) and that there is "only one relevant rationalist thinker who has a good reason to insist, as does the Antithesis [of the first Antinomy], that world is positively infinite," that is Spinoza. (80) (To avoid confusion, Boehm treats Newton as a rationalist dogmatist.)
Intriguingly, while Boehm has to explain why, given his identification of the position in the Antithesis with Spinoza's, Kant would attribute the position to "a principle of pure empiricism," my suggestion that it could just as well be Newton's faces no such quandary. (That is everything that Boehm claims about what Kant might mean with 'pure empiricism' here could also be attributed to Newton.) Moreover, when Kant [A471] identifies the Antithesis's empiricism (that goes too far) with Epicureanism (as Boehm notes on p. 105 in footnote 28), this fits, as I have argued elsewhere, Kant's pre-Critical interpretation of Newton as a kind of Epicurean. (Why he would do so I have explained here.)
So, what follows from this? Kant did, I think, distinguish Newton and Spinoza when it suited him. But in Kant's hands, Spinozism mixes elements from Newton's and Spinoza's writings. (This is not to deny that Spinoza is the more consistent Spinozist than Newton, of course.) This observation does not undermine Boehm's larger claims about the philosophical dialectic, but it does undermine his interpretation of Kant.