Proposition 23 of Part V of the Ethics says:
The human mind cannot be absolutely destroyed along with the body, but something of it remains, which is eternal.
A demonstration is offered. The scholium to the proposition adds that 'we feel and experience that we are eternal'.
These views seem to form the apex of Spinoza's system, coming almost at the end of the Ethics as the apparent culmination of a long series of connected propositions. Although they are not particularly emphasised -- Spinoza left his readers to decide what mattered -- it would seem strange to imagine that they were not of importance to him.
To commentators, these views form the apex of his system in another way: as a pinnacle of difficulty, or a stumbling-block for the understanding. Some  have just give up on Spinoza at this point, believing that he had extended himself beyond any rational defence or explanation of his position, lapsing into paradox or mysticism. Others have avoided the real problems of interpretation with rhetoric. Even Pollock, normally so lucid, offers no better than this:
Spinoza's eternal life is not a continuance of existence but a manner of existence; something which can be realized here and now as much as at any other time or place; not a future reward of the soul's perfection but the soul's perfection itself. In which, it is almost needless to remind the reader, he agrees with the higher and nobler interpretation of almost all the religious systems of the world .
In addition to the general difficulty in seeing what Spinoza meant, and how it could be fitted into a general understanding of his thinking, there are at least two particular points where his opinion in Ethics V, 23
Understanding eternity has seemed to conflict with other important views that he expressed: where he has seemed inconsistent as well as, perhaps, unintelligible.
First, most readers of Part II of the Ethics have assumed that mind and body must exist together: 'The object of the idea constituting the human mind is the body - i.e. a definite mode of extension actually existing, and nothing else' , and so on. That view has often seemed (and often seems to students exasperated by Descartes) to resolve the paradoxes created by an immaterial spirit, affected by and affecting the extended body while retaining a capacity for immortality. Admittedly, although Spinoza may have evaded the problems of body-spirit dualism, he did land himself with the apparently awkward consequence that individual things, not just people, are 'animate, albeit in different degrees'  -- but otherwise, what he said in Part II of the Ethics about the constitution of people looked fairly sensible. So how could something of the mind 'remain' when the body was destroyed? That seems to be in direct conflict with the view that mind and body must go together.
Secondly, his thinking about time was elusive and never collected into a single coherent statement. He followed a conventional enough distinction between endless duration -- the experienced passage of time -- and timelessness or eternity . The eternal 'does not admit of "when" or "before" or "after" . A natural reading is that the eternal truths of geometry and philosophy will be timeless, with no 'before' or 'after', in contrast with human experience: eternity 'cannot be explicated through duration or time, even if duration be conceived as without beginning or end'.7 In the Demonstration to Ethics V, 23, we see that 'we do not assign duration to the mind except while the body endures'. Yet we are said to 'feel and experience' that we are eternal. Feeling and experiencing hardly sound relevant to the eternal truths of mathematics or philosophy. And even if they were, what we might call their human relevance would seem to be left as problematic. The type of eternity embodied or expressed by the eternal truth of the theorem of Pythagoras is hardly a type that might offer any consolation, hope or even interest to anybody except a Pythagorean. If eternity is distinguished from experienced duration, how could we experience eternity?
Maybe there is some religious interest in any philosopher who claims to demonstrate that part of the mind is eternal -- though, even more than with Spinoza's demonstrations for the existence of God, we are not thinking of proofs to convince the wavering or the unfaithful. It might be imagined that the eternity of the mind was of special personal significance, and that a demonstration of it was a central motive behind his work; but there is not a word of evidence for that view, and no hint of it in his letters or in his mature writings other than the Ethics.
As with his remarks about Jesus, these problems might seem to be incidental in terms of his narrowly philosophical interest to us. That is a view that he did something to encourage himself. As we have seen, his passage on eternity in Part V of the Ethics appears before two concluding propositions, which tell us that 'even if we did not know that our mind is eternal', the philosophical and moral conclusions of the remainder of the book would still hold. The overt reason for that conclusion is to underline that punishment and reward in an after-life have no part to play in moral philosophy -- deep scorn is poured over such an idea -- but it does not take a great deal of suspiciousness to say that Spinoza may also have been hedging his conclusions on eternity with a proviso that they were logically optional to his other views. So, philosophically, it might not look too harmful to disregard them.
There is some philosophical, exegetical interest in the removal or explanation of the apparent inconsistencies within Spinoza's work . But the real interest surely comes from the problem of understanding what he was trying to do. This chapter is titled 'Understanding Eternity' for that reason. Suppose -- and we are not going to suppose this without reservations -- that his views could be made consistent, in that their internal discordances could be removed or explained away. Suppose that his views might be thought to be plausible, in the sense that their demonstrations were no weaker than others that we accept for the sake of comment or exegesis. We can still ask whether he succeeded in making himself intelligible: whether the type of eternal existence of the mind which he hoped to demonstrate, and which he said we experience, is of a type which we find to be of any significant value or interest.
In twentieth-century terms it may seem natural to recast this point into a linguistic sense, as a problem about 'the meaning of religious language'. The meaning of 'eternity' in the Ethics might be thought to be exactly the meaning that was constructed or created by Spinoza's apparatus of geometrical proof . And in that event, to ask whether his notion of eternity imparted any significant sense might be thought to fall into the same error as in confusing sense ('What "England" means') with significance ('What England means to me') . The meaning of 'eternity' might be thought to have been constructed exhaustively, without remainder, in the context of Spinoza's system, and so it would be an error to imagine that its 'personal significance' could be any wider or deeper, or different from its literal, systematic sense. That might seem especially so in the case of a writer like Spinoza, where precision and intelligibility might matter, and where any aura of unexplained significance might seem badly out of place.
If understanding eternity were no more than understanding how the sense of 'eternity' (rather aternitas) was assembled in Spinoza's system, that might be correct. It should be possible to see why that is not so.
We can see it best in the exactly analogous situation created by his use of the figure of Christ [….] One could claim that what he offered in the Theological-Political Treatise was, in effect, an elaborate specification of the use of the name 'Christ', whose meaning was no more than the collection of uses or applications accepted by Spinoza, and no others. So 'Christ' is used to mean 'uniquely free man', 'supreme knower', 'exemplar of holiness', but not, for instance, 'man who rose corporeally from the dead'. It is hard to know how necessary it is to say that such a reading would be bizarre. The treatment of Christ was not, of course, a form of elaborate stipulative definition of a technical term. It was some form of characterisation that modified or built up a figure already well known to Spinoza's readers. We may think that his Christ was an artificial figure, constructed and deployed for his own philosophical or religious reasons; but the figure was significant enough, beyond its name, to shock Spinoza's contemporaries and to intrigue his commentators. What he said, at least, seemed intelligible.
With eternity he may not have managed that. With the figure of Jesus we saw that there may have been some risk of making the meaning too commonsensical to be of interest - if Spinoza only wanted to point to Jesus as an exceptionally wise and gifted moral teacher he could have done that in one sentence, without the puzzling penumbra of suggestions of unique freedom and unique capacities for knowing. In a parallel way, if the eternity of the mind is, for example, only an acquaintance with eternal truths -- from geometry, perhaps -- so that the more eternal truths we know, the more 'eternal' our minds are, that might be consistent with his other positions, but it would be too banal to merit interest or attention. We can see why Jonathan Bennett could say:
Since I gave up medical studies for philosophy I have had thoughts that P, where P is necessary, more often than before the switch, and more often than I would have if I had stayed with medicine. Does my mind have a larger eternal part than it used to?... Spinoza should answer 'Yes' .
Although we can understand that Spinoza intended something less immediately graspable than individual personal survival after death, if his views have any interest they should convey something more promising than an eternal contemplation of geometry. Some notion of the eternity of part of the mind may have been constructed by him, but the problem may be in seeing why it should matter or why we should care about it.
The philosophical interest comes from how, whether or how far he was able to make the eternity of part of the mind intelligible. In an obvious sense it was a technical element in the apparatus of his system, like his infinite modes or conatus. If it was no more than that, then explaining its articulation in his system should exhaust its interest, in giving us a full grasp of what it meant.
Of two points, at least, we can be certain: that he must have regarded the eternity of part of the mind as intelligible, and that he must have wanted to make it intelligible to his readers. This is worth saying only because we can easily miss the respect in which he differed from almost every other writer on this most difficult of topics: in his refusal to admit any element of mystery or ineffability. If we fail to grasp his meaning, that may be because he failed to convey it successfully, not because he thought it was inexpressible.
The philosophical interest goes beyond a narrow one, because what applies to the eternal part of the mind may apply also to an understanding of much of Spinoza's other systematic apparatus. To take the most extreme case, God is explained, in a Spinozist sense, in the opening propositions of the Ethics, but what do we understand of Spinoza's God as a result? Literally everything, without remainder, or only a series of hints?
Once again we need to remember that we do not know why Spinoza wrote what he did. An historian of ideas might think that the demonstration of Ethics V, 23 would fit nicely in a collection of philosophical proofs of immortality of the soul, starting with those in the Phedo. Yet it is very uncertain whether Spinoza can be seen like that. At the end of the Ethics he wrote of the belief that the mind is 'eternal or immortal', but only in a context intended to deride eternal punishment or reward. A positive theological context is missing. It would be rash to assume one .
And again, there must be questions about how far a demonstration was meant to 'prove' anything to anyone (and if so, to whom). As much as in the opening propositions of the Ethics, with the 'proof of the existence of God, the Demonstration to V, 23 is one which draws together threads established in other arguments. It is hardly a persuasive proof, in the sense of convincing anybody who seriously doubted its conclusion, and it surely cannot have been meant to be one:
In God there is necessarily a conception, or idea, which expresses the essence of the human body [V, 22] and which therefore is necessarily something that pertains to the essence of the human mind [II, 13]. But we assign to the human mind the kind of duration that can be defined by time only in so far as the mind expresses the actual existence of the body, an existence that is explicated through duration and can be defined by time. That is, we do not assign duration to the mind except while the body endures [II, 8, Corollary]. However, since that which is conceived by a certain eternal necessity through God's essence is nevertheless a something [V, 22], this something, which pertains to the essence of the mind, will necessarily be eternal.
This would offer nothing by way of hope or consolation to anyone concerned about life after death. In any event, it must be plain that Spinoza did not have that in mind. To base anything in life on hope for the future would be an error for him. In addition, whatever 'remained', it was not memory -- 'The mind can exercise neither imagination nor memory save while the body endures'  -- so there could be no consciousness of personal continuity.
These negative points should be obvious preliminaries. No one should be surprised that Spinoza's views about the eternity of the mind would be as difficult to reconcile with conventionally religious positions as the rest of his thought.
In Spinozist terms, the rational support for a point of view should also be its explanation. We can ask how far the support for a view of eternal existence serves to explain it, beginning with the technical case in Spinoza's Demonstration to Ethics V, 23, and then widening the view to the more general thinking behind it.
The demonstration was quoted above. Although it refers back to a maze of other conclusions, the argumentative strategy is not complicated. Spinoza had to show two things: that there was an eternal aspect to the human mind and that this could 'remain' when the body was destroyed. The first point, while hardly being uncontroversial, only constituted a special case of other conclusions established (to his satisfaction) elsewhere. The second one was much more difficult, given the parallelism of mind and body, and was rooted in one of his most elusive areas of thinking.
The first element needed in his demonstration - that there is an eternal aspect to the human mind - should not be unexpected because, in Spinozist terms, there is an eternal aspect to everything. The technical apparatus hinders rather than helps our understanding: there is a distinction between existence and essence. God's essence is the cause of the essence of the human body, as of all bodies. There must also be an idea which 'expresses the essence' of the body: the mind . Anything conceived through God's essence will be eternal. This sort of scholastic language does not do much to help, and elaborating it further  can do even less. The basic idea is one which runs, not too obscurely, through the Ethics. For example, in the Scholium to Part II, 45, more clearly than elsewhere, existence as duration is distinguished from 'the very nature of existence' or 'the very existence of particular things in so far as they are in God'. Existence as duration is determined by the existence of other particular things. But 'the force' by which each thing 'persists in existing follows from the eternal necessity of God's nature'. In Part V , Spinoza refers back to Part II, 45, providing some further explanation:
We conceive things as actual in two ways: either in so far as we conceive them as related to a fixed time and place, or in so far as we conceive them to be contained in God and to follow from the necessity of [the] divine nature. Now the things that are conceived as true or real in this second way, we conceive under a form of eternity, and their ideas involve the eternal and infinite essence of God.
There is no need to go into any of this, in its general or in its particular applications. In the widest way, we can see that Spinoza's understanding of eternity as existence attaches eternity to substance or nature . In as much as the human mind is seen as part of nature it must be eternal.
That may be adequate as some explanation of how the mind may be eternal, but it gets us nowhere on the second, much more tricky, point of explaining the apparent schism of the eternal part of the mind from the non-eternal body. Here, Spinoza appears to be totally boxed in by his own arguments. Unequivocally, the body is 'destroyed'. As a body, it ends at death . But the mind is supposed to be the 'idea of the body'. The memory and imagination, evidently linked to bodily functions, end with death. But what does not? However we understand his views about time and eternity in general, the assertion in Ethics V, 23, sounds irreducibly temporal: 'the human mind cannot be absolutely destroyed along with the body' (such 'destroying' can only take place at some point in time) 'but something of it remains, which is eternal' -- and 'remains', again, suggests remaining in time. That surely must be so, even if we pick up the possible hint of an arithmetical remainder.
Errol Harris thinks otherwise. Of 'remaining', he writes, 'there is no need to understand it as otherwise than as meaning that there is something eternal in the human mind besides what ceases to "endure" when the body dies (as we say in arithmetic: 15/6 = 2, remainder 3). The eternity of the "immortal" part of the human mind or soul is thus not a continued duration after the death of the body, but a quality of being'  and perhaps this is right, or at least plausible. But the hint of arithmetic must also create an impression that is more empirical: if you have fifteen apples and divide them into groups of six apples you will have two groups, and three will remain. (But maybe even here, one might argue that 'remaining' is only an explanatory metaphor, to assist the comprehension of timeless arithmetic.) Whatever the logic, the rhetoric is that 'remains' (remanet), used after 'absolutely destroyed' (absolute destrui), must evoke temporal survival.
The most difficult point is expressed by Spinoza, puzzlingly, in a negative way: 'we assign to the human mind the kind of duration that can be defined by time only in so far as the mind expresses the actual existence  of the body, an existence that is explicated through duration and can be defined by time. That is (II, 8, Corollary), we do not assign duration to the mind except while the body endures' .
So there is no duration without the body. The Corollary to Ethics II, 8 […] is one of the most obscure parts in Spinoza's work. […I]n connection with possible infinite objects or constructions. The point at issue is the status of objects that do not exist. Simplifying Spinoza's example, an infinite number of rectangles may be constructed in a circle. An infinite number of rectangles cannot 'exist' (idealistically) in a human mind, because it does not have an infinite capacity. We take a dive into heavily technical language: 'as long as individual things do not exist except in so far as they are comprehended in the attributes of God, their being as objects of thought -- that is, their ideas -- do not exist except in so far as the infinite idea of God exists'.
He goes on, in contrast, to take the non-problematic case of existing finite objects: 'and when individual things are said to exist not only in so far as they are comprehended in the attributes of God but also in so far as they are said to have duration, their ideas also will involve the existence through which they are said to have duration'.
The point is not unclear when left in technical language: infinite possible rectangles plainly do not exist in any actual sense, but if we are to think of them -- if they are to be objects of thought -- they exist in so far as the infinite idea of God exists . And deciphered into the terms of Spinoza's geometrical example, the technical language seems reasonably Retrievable. The 'infinite idea of God' […] was one of his 'infinite modes' which are used ad hoc to fit exactly this purpose: of providing some non-subjective basis for infinite possible constructions. A great deal of exegesis has gone into this point , but it has a certain commonsense plausibility. There will be actual constructions and there will also be those that are available (or excluded), given the way in which objects and space are constituted.
The Infinite Idea of God
The real difficulty here does not lie in the obscurities or possible inconsistencies of Spinoza's technical exposition. We may accept fully that the pieces of the puzzle fit together . We may even accept that 'the infinite idea of God' offers a neat, non-idealistic solution for the ontological status of non-existent but possible geometrical constructions. We can even accept some element of analogy from geometrical eternity. Apparatus may have been devised to cope with the eternal availability of possible constructions. The basic problem, though, is in the decoding of the 'infinite idea of God' -- not as a technicality, to be dismantled in technical terms -- but as anything which gives us some convincing grip on a notion of the eternity of the mind. We read that 'our mind, in so far as it understands, is an eternal mode of thinking which is determined by another eternal mode of thinking, and this again by another, and so on ad infinitum', and this, as far as it goes, can be read harmlessly, in the sense that psychological phenomena have psychological explanations , except that it goes on 'with the result that they all together constitute the eternal and infinite intellect of God' .
The Corollary to which this Scholium is a note tells us that 'the eternal part of the mind is the intellect'. The articulation of Spinoza's thinking should not be in doubt. 'Part' of our minds can form part of the eternal and infinite intellect of God, in analogy with the way in which there can be eternal and infinite available constructions in geometry. And the trouble, obviously, is in the nature of the analogy. There is a non-mysterious, if not uncontroversial, sense to a notion of infinite available geometrical constructions: we can see roughly what is meant by the assertion that an infinite number of rectangles may be constructed within any circle (even if we retain some ontological qualms). But with minds, the analogy does not seem to work. Mental causality -- one mental event being caused or determined by another  -- can be accepted for the sake of argument. We can, to stretch a point, think of all of a person's mental events 'together' as a collection. To go further, we even can assume some world of thoughts, or possible thoughts, comprising everyone's thoughts and possible thoughts.
And this line of demystification takes us to at least two real difficulties. First, it has taken us away from anything which might be not only remotely consoling, but also of any imaginable human interest. So are my thoughts, or some 'part' of them, forever -- either atemporally or omnitemporarily -- part of eternal nature? That can be taken in various ways - psychologically, as when my thoughts exist; objectively, as where other people's thoughts exist; conceptually or propositionally, as where we say that the thoughts of Einstein have existed -- but none of these, shorn of rhetoric, seems worth more than a shrug of the shoulders in a philosophical sense.
Secondly, we can diagnose a more exact source of difficulty. Except as a hopeful analogy, thoughts just do not add up or 'constitute' in the same way as geometrical constructions . We can, if we like, treat all the thoughts that have been thought and will be thought as an arbitrary set; but it remains arbitrary. So to be told that my mind is part of the infinite intellect of God  is not to be told very much; or at any rate it is not to be told anything very exciting. (A world of thought which is only an arbitrary collection of past, present and future ideas may be logically innocuous, but is a good deal less dramatic than a Hegelian Weltgeist .) On the other hand, it might be helpful in a negative sense, in what it rules out. Spinoza's God, for example, is not thinking any thoughts which are not thought by people. In a letter, we find a statement in wholly impersonal terms, relating to nature rather than God:
As regards the human mind, I maintain that it, too, is a part of Nature; for I hold that in Nature there also exists an infinite power of thinking which, in so far as it is infinite, contains within itself the whole of Nature ideally, and whose thoughts proceed in the same manner as does Nature, which is in fact the object of its thought .
The function of the infinite intellect of God is not to think unthought thoughts, in the way that Berkeley's God perceives unperceived percepts . Non-existent possibilities, for Spinoza, are not 'thought' by God, in any recognisable way. They are 'comprehended' or 'involved in' ideas of existing objects. This is not at all clear -- some might wish to express the point, with only a dubious gain in clarity, in logical terms of 'entailing' or 'following from'  -- but we can be reasonably certain that Spinoza was not diluting a hypothesis of existing possible worlds into one of existing possible ideas. Because of this lack of logical detail, idealist readings of his position tend to rely on rhetorical posturing. For example: 'In our essential being... we realize our oneness with God, or God is expressing himself in us. And this means that in our clear and adequate consciousness we are eternal: we have attained to the kind of eternity which characterizes human nature. In this sense, our mind -- as an adequate, significant thought in the context of God's thinking -- is part of the complete intelligence of God' .
More to the point, there is a major drawback to any understanding of Spinoza's view of eternity as a merging of part of the mind into a stream of divine consciousness. Although, as we have seen, the eternity of part of the mind implies nothing about the continuity of individual consciousness, it does include some undeniable element of personal identity. My thoughts and memories, in Spinoza's view, will not survive after death; but there will still be something of me that will 'remain'. Eternity will not consist in losing identity in a Weltgeist. The most serious obstacle to idealist readings of Spinoza […] was the real, separate existence of individuals. With 'ideas', the point is more muted and much less distinct, but we can be sure that Spinoza gave no encouragement to any diminution or loss of individuality in the 'infinite intellect of God'. This must also apply to a loss of individuality in some form of 'transcendence' , a notion Spinoza repudiated so strongly elsewhere that he is hardly likely to have embraced it here One commentator has noted that 'most of what Spinoza has to say about individuation in the Ethics and elsewhere is expressed in terms of individual bodies' . It is striking that the Demonstration to Ethics V, 23, on the eternity of part of the mind, sets off from 'the essence of the human body': 'In God there is necessarily a conception, or idea, which expresses the essence of the human body'. The same approach is repeated in the Scholium: 'As we have said, this idea, which expresses the essence of the body under a form of eternity, is a definite mode of thinking which pertains to the essence of mind, and which is necessarily eternal.' And Spinoza refers back to the preceding Proposition, also rooted in the body: 'there is necessarily in God an idea which expresses the essence of this or that human body under a form of eternity'.
This might seem strange, or unnecessary, in that he could as well have started directly from the mind, not the body. What he seems to be suggesting is that it is the individual's body which is the origin or source of identification. The point is not that the body has an anti-Cartesian epistemological priority over the mind -- that we know it first -- but that the idea or ideas which make up an individual mind acquire their identity by being ideas of a particular body (rather than of several bodies, or no bodies at all). And it looks as though Spinoza wanted that sort of identity or individuality to 'remain' even when a body had been destroyed. This was imparted in an ornate terminology of actual essences, but the basic thought is a fairly simple one. As Donagan puts it, 'Ultimately, individual human minds differ from one another because the individual bodies whose affections are the objects of their primary constituents are different' . If this was indeed Spinoza's case, it was an interesting one: presumably the thought would be that the body is necessary at some time for identity, but not the continuing existence of the body. Rather, the appeal would be to something like an identity with the unity of ideas associated with a past body, or a body that had a duration at a particular time . It would be an exaggeration to say that we can find a well-worked-out defence for this view in the Ethics. The view is probably there , but a solid defence for it is not.
What is clear and certain is that Spinoza attached the highest importance to individual knowledge: 'The more we understand particular things, the more we understand God' . And it is hard to read this in any way except as meaning that a knowledge of the individual detail of nature is what matters. In theological terms, the way to God is not by losing the identity of the self in generalities or abstractions: it is by discovering specific, concrete knowledge. But this should not be taken as an ideology of empirical facts. Spinoza was not a proto-positivist.
He stresses the superior power of what he has called 'intuitive' knowledge, or 'knowledge of the third kind'. This forms a specific connection between a knowledge of individuals and eternity. A general proof that everything depends on God, for example: 'although legitimate and exempt from any shadow of doubt, does not so strike the mind [non ità tamen Mentem nostram afficit] as when it is inferred from the essence of each particular thing which we assert to be dependent on God' . An intuitive grasp of individual truths -- not a general, mystical view of nature -- is what brings us nearest to eternity.
This takes us to the experience of eternity: the remark that 'we feel and experience that we are eternal', which has caused such enormous exegetical difficulty .
It is worth seeing that Spinoza does not need to prove anything about our 'experience' of eternity, nor does this experience appear as a conclusion from any proof offered by him. The assertion that 'we feel and experience that we are eternal' is offered as a datum, not as a theorem or an hypothesis . Its support is left undetermined. One explanation for this might be that the demonstrated eternity of part of the mind somehow made possible a feeling and experience.
This might be taken loosely, as offering a theoretical substructure for a kind of experience reported along similar lines from many different sources, some of them mystical. The thinking might be that many writers have reported intimations of immortality, often in language far removed from precise logic, but here is what enables such feelings to have some sense: the mind has some element of eternity, after all, and it has ways of knowing which allow direct glimpses of eternal truths. Such a vague account does have two advantages.
First, it does allow for a kind of intuition which has proved extremely difficult to accommodate within critical theories of knowledge -- but without providing any general legitimation or endorsement. Remarkable intuitions or insights -- mathematical, musical, personal or religious - may after all occur, and any account of human experience which excludes them may be defective.
Secondly, it may indicate, if only in outline, how Spinoza bridged the gap between what we experience in duration and what we know in eternity. Experience must be in time, at a particular time. So experience of eternity is, as Macherey puts it, a veritable oxymoron. But Spinoza does not offer experience of eternity as any kind of proof of eternity. He says that 'we' have the feeling and experience. The surrounding propositions and demonstrations indicate ways in which such experience can be understood.
This reading seems to be supported by the order of thought in the Scholium to Ethics V, 23:
it is impossible that we should remember that we existed before the body… Nevertheless, we feel and experience that we are eternal. For the mind senses those things that it conceives by its understanding just as much as those which it has in its memory. Logical proofs are the eyes of the mind, whereby it sees and observes things. So although we have no recollection of having existed before the body, we nevertheless sense that our mind, in so far as it involves the essence of the body under a form of eternity, is eternal, and that this aspect of its existence [aternam esse, & hanc ejus existentiam] cannot be defined by time...
So, in grasping or knowing individual 'eternal' truths, we have an experience of eternity. This suggests a kind of Kantian argument: that the metaphysical structure of essence and existence makes the experience possible . Because some aspect of our minds is eternal we are able to have access to eternal knowledge. But in contrast with what we would expect in a Kantian transcendental argument -- a makes b possible, b is a condition for a -- there is no sign of a counter-argument running in the opposite direction: because we are able to have access to eternal knowledge some aspect of our minds is eternal. Spinoza never argues from experience. It may be evidence, but it is not support or proof.
Maybe this gives what we might call an enabling mechanism for an experience of eternity, and may even give some shadow of intelligibility to Spinoza's views, but there seem to be two important objections.
First, even if we want to accept that there is any point in describing some truths as 'eternally true', it appears to be an unbearably ad hoc approach to say that we need an eternal apparatus to register eternal truths. Couldn't we start from an opposite angle and say how remarkable it is that wholly mortal minds are able to encompass eternal truths?
Secondly, there remains the difficulty that a grasp of many eternal truths would appear to the prosaic critic to offer only an unpromising, unconsoling form of eternity. Even if we take a more generous view of this than Bennett, awkward factual questions can come up. 'Through the greatness of the universe which philosophy contemplates, the mind is also rendered great' sounds splendid , but seems to be valid only in some circular sense: that a great mind is one that has great thoughts. Can I really become more eternal by acquiring more eternal truths? Even if we allow that the apparatus is plausible, how plausible is the project?
A response to the first of these objections would require a long detour through Spinoza's theories about knowledge, but the basic outline is straightforward. To the question: how are we able to know necessary -- that is, eternal -- truths? the answer given by Spinoza, as by Descartes, was that we share in a divine perspective: part of our minds must share a divine eternity. But the crucial difference, which removes the unsatisfactorily ad hoc quality from Spinoza's answer, is that for him the divine perspective, or the divine mind, is entirely immanent. We do share in the divine mind by knowing necessary truths, but no shares are left over for God alone. An increase in human knowledge or understanding is also an increase in the 'infinite intellect of God'. It is possible to argue that 'man possesses knowledge of objects only under the condition that he is part of the infinite intellect' , in the sense only that knowledge is supposed to be indefinitely expandable.
But if something along these lines is right, it seems to make the second difficulty more, not less acute. If the divine perspective is  the perspective of human understanding of necessary or eternal truth, it sounds intolerably banal to say that we become more eternal as we acquire more necessary or eternal truths. Bennett's jibe that he would have become more eternal by acquiring more necessary propositions would be reinforced.
But the point -- of course -- must be that it is not just any necessary or eternal truths that we acquire. Spinoza never says this explicitly, but his sense is surely not that we can undergo some kind of empirical treatment to acquire eternity by deciding to obtain as many truths as possible: 1 + 1 = 2, 1 + 2 = 3, 1+3 = 4... What he has in mind is an orderly and systematic understanding of nature. That will, for the physical world, mean mathematical physics, and for the human and moral world -- 'those things that can lead us as it were by the hand to the knowledge of the human mind and its utmost blessedness'  -- it will mean the understanding of nature elucidated in the Ethics -- and then 'in so far as we rightly understand these matters, the endeavour of the better part of us is in harmony with the order of the whole of Nature' .
It should be possible to be more specific than that, but the particular detail has to be speculative. The general picture appears reasonably certain: in understanding how nature is, how we are part in it, we acquire a view which is less bound by duration and more derived from a perspective of eternity.
But this can still sound trite, especially if it goes no further than thoughts of the empirical effectiveness of a psychological therapy. A free man thinks of death least of all things, and his wisdom is a meditation of life, not of death'  -- does this work in the doctor's waiting-room? There may be some suspicion that such blunt objections can be raised against even the most carefully shaded interpretations:
The Spinozistic mind aspires to understand itself as an integral part in a total unified articulation of the world, sustained by the necessary being of substance. It is the mind's recognition that it has such a place in a systematically unified order of thought that sustains the Spinozistic reconciliation to finitude. What is supposed to reconcile us to death is the perception of the mind as part of a systematically interconnected totality of thought, a unified 'idea' .
A reading with more ramifications -- and therefore one which goes well beyond a suspect psychotherapeutic prescription -- is suggested by Pierre-François Moreau -- J'éprouve ma finitude, donc mon éternité  -- I experience my finitude and thus my eternity. He latches on to the point of Spinoza's remark that 'we' feel and experience that we are eternal. The claim is not that we feel and experience that eternal truths exist. The feeling and experiencing, he thinks, is not the knowing of a necessity, but an awareness of our contrasting finitude which accompanies such knowing . Descartes, he says, regarded the finite as a reasonable starting-point in his thinking; but for Spinoza, finitude would not start from our limitations: on the contrary, the thinking is reversed and the finite is grounded in the infinite . We understand our feeling of finitude only through a wider understanding of infinite (and eternal) nature. Moreau's reading does not suggest that our experience demonstrates anything about eternity, directly or indirectly, and that must be correct. But it can set us off on a quest for an eternity 'at the same time promised and given, that is to say the path which will lead us towards knowledge and beatitude' .
The famous final words of the Ethics warn us that all things excellent are as difficult as they are rare. 'What is so rarely discovered is bound to be hard.' It is not a truism to tie together the difficulty of understanding Spinoza's thinking on eternity and the difficulty, which he underlines himself, in his philosophy. Some may experience eternity. Anyone could have such experience. But to understand what eternity is, we need to understand God or nature, which is not easy, and not for everyone.
Mason, Richard. The God of Spinoza. A philosophical study, Cambridge University Press, Cambridge, 1999, pp. 224-230, 234-246.
1.Notably Bennett, A Study of Spinoza's Ethics, §82, §85.
2.Pollock, Spinoza, His Life and Philosophy, p. 294.
3.Ethics II, 13.
4.Ethics II, 13, Scholium = G II 96/28: omnia, quamvis diversis gradibus, animata... sunt.
5.In a rare reference to the topic in the Theological-Political Treatise, 'the common people, prone to superstition', prize 'the legacy of time above eternity itself, temporis reliquias supra ipsam aeternitatem amat: S 54-5 = G III 10/22-4.
6.Ethics I, 33, Scholium 2 = G II 75/12-13.
7. Ethics I, Definition 8, Explication, cited at V, 29, Demonstration = G II 46/4-5 and 298/19-20.
8.It is striking that the eternity of the mind is one of the few areas in his work that has received equally valuable attention from Anglo-American writers and from those working in French: see A. Matheron, 'Remarques sur l'immortalité de Fame chez Spinoza', Les études philosophiques, 1972; A. Donagan, 'Spinoza's Proof of Immortality', in Grene (ed.), Spinoza: A Collection of Critical Essays and Spinoza (New York: Harvester Wheatsheaf, 1988); R.J. Delahunty, Spinoza (London: Routledge & Kegan Paul, 1985), Chapter IX; D. Steinberg, 'Spinoza's Theory of the Eternity of the Human Mind', Canadian Journal of Philosophy, II,1981; Moreau, Spinoza: L'expérience et I'éternité, Part III.
9. 'We need ... to speak in more detail of how to interpret a text in terms of its immanent meanings - that is, in terms of the meanings immanent in the religious language of whose use the text is a paradigmatic instance': George A. Lindbeck, The Nature of Doctrine: Religion and Theology in a Postliberal Age (London: SPCK, 1984), p. 116.
10. This point is spelled out in R. Trigg, Reason and Commitment (Cambridge University Press, 1973), pp. 50-3, and, intimated, in connection with Spinoza, none too distinctly in G. Floistad, 'Experiential Meaning in Spinoza', in J. G. Van der Bend (ed.), Spinoza on Knowing, Being and Freedom (Assen: Van Gorcum, 1974).
11. A Study of Spinoza's Ethics, pp. 362-363.
12. Ethics V, 41, Scholium = G II 307/23. Moreau finds this sole reference to immortality 'very vague and negative': Spinoza: L'expérience et I'éternité, p. 535. References in Spinoza's early works do not help us to see what he meant: for example, Short Treatise, II, xxiii and Appendix II; Principles of Philosophy Appendix II, xii.
13. Ethics V, 21, based on II, 18, Scholium.
28. Pierre Macherey points out, usefully, that Spinoza's mention of 'part of the mind (ejus aliquid G II 295/15) is misleading in that existence and essence are not two distinct parts (or 'somethings', more like the Latin) of things: Introduction a I'Éthique de Spinoza: La cinquieme partie, p. 129. Spinoza was trapped by his own terminology here: he could not write in terms of 'aspects' or 'conceptions'.
29. Delahunty gives a full analysis, though one which concludes that Spinoza's proof was 'a botched job': Spinoza, pp. 295-300.
30. V, 29, Scholium.
31. See Chapter I, pp. 38-9 above; Ethics I, Definition 8. Also Letter 12: a slightly different perspective -- 'It is to the existence of Modes alone that we can apply the term Duration; the corresponding term for the existence of Substance is Eternity, that is, the infinite enjoyment of existence or -- pardon my Latin -- of being' L 102 = G iIV 54-5.
32. Its parts may be disposed in a different way – Ethics iIV, 39, Scholium -- but its direction, conatus, as a living body, will be lost. Spinoza certainly did not think that the eternal part of the mind was the 'idea' corresponding to the dust and bones of a dead body.
33. 'Spinoza's Theory of Human Immortality', in Mandelbaum and Freeman (eds.), Spinoza: Essays in Interpretation, p. 250.
34. A parallel line of argument pursues the distinction between 'actual' and 'formal' existence and essence - see Delahunty, Spinoza, pp. 295-300, referring to Donagan.
35. Ethics V, 23, Demonstration = G II 295/20-4. Shirley's translation places the reference to II, 8, Corollary at the end of the sentence.
36. Spinoza's negative way of putting this - they do not exist except in so far as the infinite idea of God exists -- non existunt, nisi quatenus infinita Dei idea existit, G II 91/7, is logically equivalent but rhetorically more cautious.
37. See, for example, Yakira, 'Ideas of Nonexistent Modes', with the copious further references given there.
38. Alexandra Matheron assembles the most systematic apologia, ending: 'Indeed, we can regret that Spinoza included this doctrine of immortality in his system. We can also ask ourselves about the reasons for this inclusion. But it is a fact, the doctrine is there; and it is in accordance with the system': 'Remarques sur l'immortalité de l'ame', p. 378.
39. From Ethics II, 9, which is itself a special case, expressed in psychological terms, of the general argument in I, 28, that all finite individuals are only determined by other finite individuals.
40. Ethics V, 40, Scholium. The 'infinite intellect of God', Dei aeternus, & infinitus intellectus, is an infinite mode.
41. As at Ethics II, 9.
42. 'This view of the human mind as but one idea in the infinite intellect of God is at first sight even more bizarre than the human body's alleged containment in larger individuals, reaching up to the universe as a whole': Genevieve Lloyd, Part of Nature: Self-Knowledge in Spinoza's Ethics (Ithaca: Cornell University Press, 1994), pp. 16-17.
43. Ethics II, II, Scholium.
44. Though not on the low-key reading given in Craig, The Mind of God and the Works of Man, pp. 179-80.
45 Letter 32 (1665), L 194-5 = G IV 173-4.
46. The point of similarity is in terminology: both Berkeley and Spinoza use ideas, but in wholly different ways: surely a sign that the term was bearing too much weight.
47. See Yakira, 'Ideas of Nonexistent Modes', pp. 162-9.
48. Joachim, A Study of Spinoza's Ethics, pp. 301-2. A devastating critique of the kind of part-and-whole intimated here was given by G. E. Moore in Principia Ethica (Cambridge University Press, 1903), §22.
49. As in Harris, 'Spinoza's Theory of Human Immortality', p. 261: 'the mind's transcendence of the body's finite limits... a transcendence characteristic of idea as such'.
50 Lee Rice, 'Spinoza on Individuation', in Mandelbaum and Freeman (eds.), Spinoza: Essays in Interpretation, p. 195. This is also well stressed by Pierre Macherey, Introduction a l’Éthique de Spinoza: La cinquieme partie, pp. 125-6 and Alexandre Matheron, 'La vie éternelle et le corps selon Spinoza', Revue philosophique, 184, 1994.
51. Spinoza, pp. 191-2. See also Lloyd, Part of Nature, p. 135.
52 This could be seen, critically, as getting the benefit of the powerful considerations given by Bernard Williams for the necessity of the body in questions of personal identity while evading the necessity for bodily continuity ('Personal Identity and Individuation' and 'Bodily Continuity and Personal Identity', both in Problems of the Self). Amihud Gilead gives an extremely abstract treatment in 'Spinoza's Principium Individuationis and Personal Identity', International Studies in Philosophy, vol. 15/1, 1983.
53. Donagan refers to Ethics II, 17, Scholium = G II 105/30-106/9.
54. Ethics V, 24: Quo magis res singulares intelligimus, eb magis Deum intelligimus.
55. Ethics V, 36, Scholium = G II 303/16-25.
56. 'uneformule particulierement frappante, qui a fait couler beaucoup d'encre... Cette formule a l’allure stylistique d'un véritable oxymore, associant des elements qui paraissent incompatibles...' Macherey, Introduction a I'Éthique de Spinoza: La cinquieme partie, p. 131; or, in contrast, 'a strikingly figurative expression, which may seem out of place in the austere surroundings of the Ethics', Parkinson (ed.), Ethics, p. 284, n. 171.
57. And it is 'we' who feel and experience, not a Cartesian 'I' [….]
58. Diane Steinberg argues a stronger case, 'that Spinoza came to hold that a part of the mind is eternal in order to account for the mind's ability to have adequate knowledge and knowledge under the form of eternity': 'Spinoza's Theory of the Eternity of the Human Mind', p. 65. This applies to the second -- scientific -- as well as the third -- intuitive -- form of knowledge.
59. From the Spinozistic closing words of Russell's Problems of Philosophy.
60. Bartuschat, 'The Infinite Intellect and Human Knowledge', p. 206.
61. Just is, not is nothing but: the point is not a reductive one. Again, for Spinoza, the divine perspective can be a human one but the human one can also be divine.
62. Ethics II, prefatory paragraph. The physical alternative is sketched in the sections between Part II, Propositions 13 and 14.
63. Ethics, IV, final lines.
64. Ethics, IV, 67.
65. Lloyd, Part of Nature, p. 137.
66. L'expérience et I'éternité, p. 548; éprouve helpfully suggests proving and realising as well as experiencing.
67. Ibid., pp. 547, 543.
68. Ibid., p. 546.
69. Ibid., p. 549.