Locke on the Soul
Locke maintains the ontological neutrality of his theory of ideas and substances. That is, the theory should be compatible with different beliefs about what the objects of those ideas may be. For example, the impossibility, or at least very great difficulty, of deciding one way or the other the views of materialist philosophers to the effect that everything is extended matter (to which modifications such as solidity may be added) provides a good reason that a theory of knowledge, or any other philosophical theory, be compatible with an outcome that those materialist views are either completely or partially correct or completely wrong. While the theory of ideas and substances in itself respects that neutrality, Locke, in the course, of the many chapters of his Essay Concerning Human Understanding, frequently dives into the ontological quagmire. In one instance Locke attributes to Descartes the ontological view that material objects are defined as extended only and champions a revised view that material objects are extended and solid and that extension without solidity is empty space.
Equally, much of Locke’s treatment of the mind or soul is aimed squarely at showing that, as far as his theory of ideas and substances is concerned, the mind or soul could very well be either thinking matter or some other sort of thinking substance that is not matter (pp. 440 ff.). However, in his proof of the existence of God, Locke veers from a demonstration that the creator of the soul cannot be material to a statement that the soul is also probably not material.
I am not conversant with the publishing history of the Essay (though Editors’ notes show no substantial revisions in this regard between the first and the later editions when Letters to the Bishop of Worcester were inserted), nor am I privy to the layers of developing views that may have been deposited in the text during its composition. But it does appear that at first Locke composed a coherent and unified text that was meant to demonstrate the ontological neutrality of his theory of ideas and later, either at the prompting of his own internal angels or simply to appease the Worcesters of the land, inserted the demonstration of the "great probability" of the immateriality of the soul.
Assertion of Neutrality. Appearances to the contrary, there are in fact not many arguments in the Essay. Rather it consists in the statement of a broad theory (of ideas, faculties, knowledge and mind) and the drawing of the consequences of that theory, or, at least as regards the materiality of the soul, showing what consequences the theory does not have. Nevertheless it is worth recalling how Locke presents his assertion of ontological neutrality and what reasons, if any he gives for defending this assertion.
Locke admits a distinction between the concepts of man and person (or self). These concepts are distinct because the criteria of identity (the respect in which we say something is the same man or person) are different. Being the same man (maintaining a single biological organization despite change in material parts) is not the same as being the same person (maintaining a unity of consciousness, a belief that different experiences are all my own). At this point he introduces an unexpected distinction between a person and a thinking substance. This is unexpected because the notion of a person was not introduced in his chapter on substances, and, if the concept of person is defined as it is here as a unity of consciousness, person and thinking substance should be the same. But Locke asks whether the criteria of identity for a thinking substance differ from those of a man or a person as a way of showing what must be proved in order to prove that thinking substances are immaterial. "…those who place thinking in an immaterial substance only…must show why personal identity cannot be preserved in the change of immaterial substances…as well as animal identity is preserved in the change of material substances…." (p. 248) Can there be different immaterial substances in one person or different persons in one immaterial substance? "That cannot be resolved but by those who know what kind of substances they are that do think…," that is, "till we have clearer views of the nature of thinking substances" (pp. 248-249). It is possible (but unlikely) that agents (immaterial substances) other than myself could have performed the actions I remember having done. Similarly it is possible but unlikely that a spiritual substance "stripped of all it memory or consciousness of past actions" is part of the person any more than any "particle of matter" separated from the body is part of the man. "…let men according to their diverse hypotheses, resolve of that as they please" (pp. 255-256). So the apparent distinction between spiritual substance and person falters due to a lack of a distinct criterion of identity for spiritual substances.
A man is a kind of organic unity of material parts, and so he is likely to be wholly or mostly material. A person or a self can be wholly material or at least partly immaterial. If I am aware of myself as the same self, thinking something now and thinking something in the past, I am the same self, "place that self in what substance you please." "Self is that conscious thinking thing (whatever substance made up of, whether spiritual or material, simple or compounded, it matters not) which is sensible…and…concerned for itself as far as that consciousness extends." (p. 251) So consciousness can be attached to something entirely material, such as the materialists believe, or adhere to something else that is not material, as Descartes believed. Materialists consider unity of consciousness to be wholly dependent on a certain "purely material, animal constitution" (p. 248). An immaterialist would hold that substantial identity can be maintained despite a change in the animal organization of the man just as animal or human identity can be changed despite a change in the atoms that constitute the man’s body. This latter position, however, can also be maintained in an ontologically neutral way if personal identity is viewed as a - possibly materially dependent - unity of consciousness. So a committed immaterialist would also have to maintain that the identity (viz. existence) of a spiritual substance is independent of identity as a person. The theory is fairly clear, but two of Locke's statements could stand some revision to avoid confusion. The first reads, "...the substance, whereof personal self consisted at one time, may be varied at another, without change of personal identity," (p. 248) to which the following could be added by way of clarification: "as long as varying the substance of the personal self is understood strictly as interchanging individual memories or conscious states, as when part of an animal's body is chopped off, and does not mean the complete substitution of every memory and state of consciousness by different memories and states." Likewise, the sentence about the materialists that reads, "...they conceive personal identity preserved in something else than identity of substance," (ibid.) would better read, "they conceive personal identity preserved in something else than identity of a thinking substance distinct from the person," or better yet, "distinct from personal substance." The unclarity in these passages may arise from Locke's attempt to accommodate the Cartesian distinct between animal unity of consciousness and human unity of consciousness.
Locke’s concepts of man and person are ontologically neutral. That is, men and persons may be completely material entities or they may be composed of some mixture of the material and immaterial, or, in the case of persons, be wholly immaterial. Considering that the controversy between materialists and Cartesians appeared to be undecidable, this was a good position for a philosophy of mind that would not be shaken by some sort of clear decision one way or the other.
The way we treat reward and punishment intimates that we regard a spiritual substance as equivalent to a person. It is the unified consciousness and not a poorly defined substance that is responsible for his actions. "In this personal identity is founded all the right and justice of reward and punishment; happiness and misery being that for which everyone is concerned for himself, not mattering of what becomes of any substance not joined to or affected with the consciousness." (p. 252)
Locke reinforces the ontological neutrality of the notion of a spiritual substance as far as Xtian dogma is concerned since nothing in his theory contradicts the possibility that a body (as long as "same body" is not taken in the Worcester sense of "exactly the same ‘particles’" as composed the body at the moment of death) and a person may be just as immortal as an immaterial soul. An immaterial and a spiritual substance are not the same thing; and "…the general idea of substance being the same every where, the modification of thinking , or the power of thinking joined to it, makes it a spirit, without considering what other modifications it has, as whether it has the modification of solidity or no." (p. 458) In fact a material spirit may be immortal just like an immaterial spirit (p. 459).
Locke’s theory is fairly straightforward as far as it goes and – setting aside broader issues concerning his theory of substance – apparently unexceptionable. Locke raises the specter of an immaterial substance just to knock it down. In the end there is not a clear enough understanding of an immaterial soul to justify the distinction between a person and an immaterial soul. The distinction is indeed superfluous. There is no parallel distinction with respect to material substances, which Locke regards as the underlying substrata beneath collections of secondary qualities. The substance gold is the support of gold’s secondary qualities. Likewise the substance of consciousness should be the support of the mental activities we perceive upon reflection. There is no unified goldness whose criterion of identity is different from that of the substance gold as, upon the immaterialist ontology as described by Locke, there would be an immaterial soul whose criterion of identity is different from that of the person and his unified consciousness.
Locke raises the distinction between person and thinking substance by considering the phenomena of forgetfulness and of sleep (The sentence on p. 247 beginning, "But that which seems to make the difficulty is this...." introduces the issue). Forgotten states of consciousness (viz. forgotten memories), when remembered, are part of my person. But these forgotten memories are thinking substances. Locke poses the question, are they immaterial substances? Likewise, during periods of nconsciousness such as sleep we have no consciousness at all and therefore no unity of consciousness. But my thinking substance supposedly persists during unconsciousness. However, neither of these phenomena offer any reason why we should consider the existence of immaterial thinking substances independent of the substance of the person. To the extent that two substances can be considered at all because of forgetfulness, that is only because one substance is at some point part of the other. The forgotten state of consciousness is or was a part of the person's unified consciousness, just as a severed finger was a part of the man. If the severed finger can, following Locke, be considered to have its own purely material substance while having been a part of the man that maintained his animal substance both before and after the finger was severed, so can the forgotten state of consciousness, be considered to have its own thinking substance while having been a part of the person that maintained his personal substance both before and after the memory was forgotten. In both cases we are dealing with a part-whole relationship and not with an intimation that there may be two distinct substances of the whole (a personal and a thinking substance) because the part and its substance can be subtracted. Sleep and other total interruptions of consciousness can be more problematic since there is no direct analogy to material substance where complete disappearance in space for a period of time might lead us to conclude that what reappeared was a distinct substance from what had disappeared. But this disanalogy does not force us to conclude that there is a thinking substance entirely coextensive with the person but yet distinct from that substance which is the substrate of the person. It can as easily be understood by noting that the criterion for identity of a person is just different from the criterion of identity for a material object.
The immaterialist could justifiably reject Locke's challenge that he furnish criteria of identity for thinking substances which are distinct from the criteria if identity for a person. He could point out that the thinking substance is an unknowable substratum of the person and his organic unity and ideas of reflection, just as the material substance of a piece of gold is an unknowable substratum of gold's secondary qualities. Since substances are unknowable according to Locke, then the kind of identification Locke demands for spiritual substances is by definition impossible. After all, the criterion of identity Locke proposes for inanimate objects is just existence without further explanation. We say animals are something distinct from their parts just because we intuitively recognize the difference. In the same way the immaterialist can claim he intuitively recognizes the difference between an animal and a man with a soul without providing any further clarification. To this extent Locke's distinction between personal and spiritual identity does not suffice against the mere ungrounded assertion of the existence of a non-animal soul. If Locke intends to direct his challenge against one or more proofs of the substantiality of the soul, it would be better to examine those proofs on their own merits and refrain from erecting abstract counter arguments which could be rejected. If Descartes' views are at issue, it is worth noting that Descartes really stops somewhere between a sheer assertion and something like a proof. Descartes indeed understood the Cogito to prove his own existence and he understood that proof to lead to the further consequence that he was not a material body since he can doubt the existence of material bodies but not his own. (Of course, it could turn out that the indubitable entity was all along something whose existence you had originally doubted just as, according to Descartes, the soul turns out to be the product of a benevolent God all along even though this was in doubt at the stage that he proved his own existence: This is where Descartes' proof of the immateriality of the soul breaks down.)
The very notion of a Lockean substance is, at least partially, a theoretical construct, devised partly to help explain the gap between material objects and what we perceive (or sense) in material objects, namely their secondary qualities, and partly to explain the persistence of a (same) object espite a change in its parts. The notion of a thinking substance, whether that substance be the substrate of a unified consciousness or something wholly distinct, serves the first goal not at all. Consider: a thinking substance is not a support for a mind’s secondary qualities (viz. its perceived mental acts) because minds do not have qualities that are accessible to anyone except the person himself. So either there is nothing to sense (if you are a different person) or no gap at all between what you perceive (through reflection) and what causes your perceptions. Indeed there is no need to hypostatize an underlying thinking substance, distinct from the animal unity of the person, as long as we do not distinguish between the ideas we perceive upon reflection and the cause of those ideas as we do in the case of material objects and their primary and secondary qualities. The problem now is that, like the ideas of reflection themselves, the cause of those ideas is evident to only one person. The exception to this would be if we adopted a strictly materialist position and assumed a correspondence between our ideas and our brain states. In that case, one class of secondary qualities would be our ideas such as we sense through reflection. The primary qualities would lie in our neurons and the biological structure of the brain. Note, however, that there would be a second class of secondary qualities composed of the colors, shapes etc. of the brain cells observed by the biological scientist. One class of secondary qualities would only be observable by one person while the other would be observable by many. A consequence of this arrangement of the theory of ideas and substances should lend support to the probability that the soul is material. For, by a parallelism with the substance of clearly material objects like gold, the primary qualities underlying the secondary qualities of our mind we perceive upon reflection would be extended and solid matter, namely the brain and its structure, just as the primary qualities underlying the secondary qualities of gold we perceive through sensation would be extended and solid matter, the particles arranged according to the atomic structure of gold.
The Immateriality of the Soul. Locke’s theory is neutral with respect to the immateriality of thinking substance. But he does believe he has a proof that the immateriality of the soul is "very probable" (pp. 458 and 475). The first step is his cautious assertion that it is possible that thinking substance be something other than material substance. But he adds a wrinkle to this bare statement of possibility that purports to move possibility into acceptability. And the new wrinkle is not without problems. Locke adds that anyone, who would consider the notion of spiritual substance to be unacceptably vague, should consider that it is no more vague than the notion of a material substance. "…the idea of a corporeal substance in matter is as remote from our conceptions and apprehensions as that of spiritual substance or spirit; and therefore, from our not having any notion of the substance of spirit, we can no more conclude its non-existence than we can, for the same reason, deny the existence of body…." (p. 210). There is trouble in this adjustment, however, for, even though the ideas of sensation and the ideas of reflection are equally within the mind, the substrate of our ideas of sensation lies outside the mind, while the spiritual substrate of our ideas of reflection remains within the man (Locke says that my spiritual substance is "within me," p. 216). Material substances have an extra-mental, shall we say, objective reference that spiritual substances do not. We cannot know whether or not a piece of gold causes the same ideas (viz. secondary qualities) in my neighbor as it does in me, but even entertaining this doubt involves the assumption that my neighbor and I sense the same piece of gold and that this substance gold is outside both of us, however ultimately unknowable it may be. For we could not even sense the substance gold through the agency of its secondary qualities if it were inaccessibly locked away in either one of us as our souls are supposed to be. If the substance gold were somehow inaccessibly locked away within me, it could not hardly cause ideas of its secondary qualities in my neighbor. The situation is different with my soul. My neighbor cannot even question whether my soul causes the same ideas in him as it does in me because my spiritual substance cannot be (reflectively) perceived by him as it can by me or as our shared piece of gold can be sensed by both of us. The notion of a single external and objective substance that causes two different sets of ideas (secondary qualities) in two different people is, in the Lockean scheme, an important basis on which scientific knowledge is constructed. The fact that my soul is not such an external objective substance but something entirely within me is the reason we may entertain doubt as to its real existence over and above any doubts we may have about substances in general. Locke’s very comments that one man cannot perceive or otherwise access the simple ideas in another man’s mind (Cf., for example pp. 310 & 441) have this, for him, unexpected consequence, that there is such a notable difference in kind between material and spiritual substances as to cast doubt on what value the latter may have outside of appeasing the Xtian authorities.
The next step is to take the conclusions from his proof of the existence and immateriality of God and apply them to spiritual substance such as to show the "great probability" (p. 475) that spiritual substance is also immaterial substance. In fact this great probability amounts to no more than the admission that if there exists one immaterial substance, there may be others, among which may be counted my soul. This really doesn’t do much in the way of probability; it would probably be convincing only to those who are previously inclined to believe it.