Kant and the Problem of Other Minds
1. Introduction
In the preface to the B-edition of the 1st Critique, Kant writes: “No matter how innocent idealism may be held to be as regards the essential ends of metaphysics… it always remains a scandal of philosophy and universal human reason that the existence of things outside us… should have to be assumed merely on faith, and that if it occurs to anyone to doubt it, we should be unable to answer him with a satisfactory proof” (Bxxxix). In this passage, Kant famously argues that we should be able to know – and not merely have faith – that an external world exists. In this paper, I examine how Kant would respond to an equally challenging skeptical worry, namely the problem of other minds. Is Kant as troubled by the problem of other minds as he is by external world skepticism? That is, like his reply to external world skepticism, does Kant provide a transcendental argument for the existence of other minds? Or does he think that it should be treated as a mere article of faith, just like the immortality of the soul, freedom, and God? Surprisingly, Kant’s views on this topic have been largely overlooked. I think this is unfortunate. In contrast to the existing scholarship, I show that Kant actually defends four different positions on the problem of other minds. First, I discuss a skeptical approach that Kant takes in the Lectures in Metaphysics L1. Second, I discuss a more empirical approach that Kant takes in the 2nd Paralogism. Third, I discuss what seems to be a transcendental argument for other minds defended in the 3rd Paralogism. Fourth and lastly, I discuss regarding other minds as a matter of ‘moral faith’. In the concluding section of the paper, I evaluate the pros and cons of each approach. In the end, I argue that while Kant has a lot more to say about the problem of other minds than most scholars typically recognize, none of his solutions seem ultimately satisfactory.
2. The Skeptical Approach: Other Minds in the Lectures
What is the problem of other minds? Generally speaking, it is a worry about whether other people have minds like our own. Most of us naturally believe that others have inner mental lives – that they experience the world, have feelings, thoughts, pleasures, pains, etc. – and we feel justified ascribing mental states to them. The question, however, is not whether we can correctly know another person’s thoughts or feelings. Instead, it is whether we can be rationally justified in believing that they have any at all. While we have a “privileged” first-person access to our own thoughts, we have at best indirect access to the inner mental lives of others. Seen this way, the problem of other minds generates a deep epistemological worry: How can we be rationally justified in believing that other minds even exist?
In the Lectures on Metaphysics L1 Kant acknowledges this epistemological problem. Indeed, these lectures written in the mid-1770’s are one of the few places where Kant ever explicitly addresses the problem of other minds. In his account of rational psychology, Kant discusses the nature of human beings in contrast with “other thinking natures” (28:271). Human beings are composed of (1a) a physical body and (1b) a self-conscious thinking nature. Animals are similar to human beings insofar as they have (2a) a physical body and (2b) are conscious, that is, they have sensory representations. However, they lack (2c) self-consciousness or, as Kant puts it, “the concept of the ‘I’”. Therefore have neither understanding nor reason (28:276). By contrast, angelic beings or spirits are similar to human beings insofar as they have (3a) a self-conscious thinking nature. But they differ insofar as (3b) they are purely immaterial, that is, they exist without a physical body.
Kant argues that we can only problematically assume the existence of angels (28:278). He offers two reasons why. First, it goes beyond any possible experience to know whether thinking natures in general can exist independently of physical bodies (28:277-278). Second and more importantly, spiritual beings themselves can never be an object of cognition, either of outer sense or of inner sense. With respect to outer sense, Kant explicitly writes: “They [spiritual beings] are no object of outer sense, thus they are not in space” (28:278). Spiritual beings cannot be objects of inner sense either, since inner sense only acquaints us with our own inner mental states. Thus Kant concludes: “We can say no more here [about spiritual beings]; otherwise we degenerate into phantoms of the brain” (ibid).
However, all this seems equally true about the existence of other finite minds. Other finite minds can never be the objects of outer sense. As Kant writes:
A thinking being, as such, cannot at all be an object of outer sense: we can perceive through outer sense neither thinking nor willing nor the faculty of pleasure and displeasure; and we cannot imagine how the soul as a thinking being should be an object of outer sense (28:271).
And as we noted before, we can never know about other minds through our inner sense either. Given these conclusions, Kant asks: “Are we to cognize souls that are outside of us… for which we have no data at all?” (28:275). His answer here seems wholly negative. Since other finite minds cannot be an object either of inner or outer sense, we should regard their existence as equally problematic as the existence of spiritual beings.
3. The Empirical Approach: Other Minds in the 2nd Paralogism
In the 2nd Paralogism of the 1st Critique, Kant returns to the question of other minds. Similar to the Lectures on Metaphysics, Kant argues that other minds can never be an object of outer sense. As he writes:
We can rightfully say that our thinking subject is not corporeal, meaning that since it is represented as an object of our inner sense, insofar as it thinks, it could not be an object of outer sense, i.e., it could not be an appearance in space. Now this is to say as much that thinking beings, as such, can never come before us among outer appearances, or: we cannot intuit their thoughts, their consciousness, their desires, etc. externally; for this belongs before inner sense (A358).
Kant recognizes that we cannot perceive the inner mental states of others. However, he interestingly suggests that we can infer from their bodies that they have inner mental lives. As he writes:
…thus I can also assume that in the substance itself, to which extension pertains in respect of our outer sense, thought may also be present, which may be represented with consciousness through their own inner sense. In such a way the very same thing that is called body in one relation would at the same time be a thinking being in another, whose thoughts, of course, we could not intuit, but only their signs in appearance. Thereby the expression that only souls…think would be dropped; and instead it would be said, as usual, that human beings think, i.e., that the same being that as outer appearance is extended is inwardly (in itself) a subject, which is not composite, but is simple and thinks (A359-360, emphasis added).
In this passage, Kant claims that we can view other human beings in two different ways: first, with regard to outer appearance, in terms of their physical bodies, and second, with regard to inner appearance, in terms of their nature as thinking subjects. Given this, Kant suggests that the correlation between our minds and bodies gives us sufficient grounds for inferring an inner mental life from how others behave. In this way, Kant anticipates John Stuart Mill’s famous “argument from analogy.” According to Mill, we can be justified believing in other minds based on a posteriori inductive grounds. As Mill explains:
By what evidence do I know, or by what considerations am I led to believe, that there exists other sentient creatures; that the walking and speaking figures which I see and hear, have sensations and thoughts, or in other words, possess Minds?. . . I conclude it from certain things, which my experience of my own states of feeling proves to me to be marks of it.
We can reconstruct Mill’s argument as follows:
P1. Based on my own case, I know that there is a correlation between my internal mental states and my external behavior.
P2. Other people display analogous behavior
C. Therefore, I infer, based on my own case, that there exists a similar correlation between their internal mental states and their external behavior, i.e., that they have minds similar to my own.
For example, I look at my friend Evan, notice that he looks angry, and form the belief that Evan is angry. According to Mill, this inference is grounded in the fact that when I’m angry, I behave in similar ways. From my own case, I infer by analogy that Evan is angry too. Thus, Mill argues that we can justify our belief in the existence of other minds via inductive reasoning, generalizing from our own individual case to all others.
Kant’s argument is both resembles and differs from Mill’s. Mill argues that we can consider the ‘signs in appearance’ as evidence for the fact that other people are thinking beings because we are reasoning by analogy from our own case to theirs. By contrast, Kant makes a direct causal inference that other minds exist on the basis of the ‘signs in appearance’. Unlike Mill, he does so without appeal to analogy. In the end, however, Kant and Mill both assume that external behavior is sufficient grounds for inferring inner mental states in others.
4. The Transcendental Approach: Keller’s Reading of the 3rd Paralogism
Do we find any transcendental arguments for the existence of other minds in Kant’s writings? Pierre Keller interestingly suggests that we can find one in the 3rd Paralogism. At A362-3 Kant writes, “But if I consider myself from the standpoint of another (as an object of his outer intuition), then it is this external observer who originally considers me as in time… the time in which the observer posits me is not the time that is encountered in my sensibility but that which is encountered in his own…” Based on Kant’s claims, Keller argues that an appeal to other minds is required for establishing objective knowledge of our identity over time. We can formulate Keller’s argument as follows:
P1. One’s identity over time can be grounded either in a 1st person or a 3rd person perspective (p. 175)
P2. It cannot be grounded in a 1st person perspective, because, from the 1st person perspective alone, I cannot distinguish between what seems to be the case from what actually is the case about my identity over time (p. 176)
P3. Therefore, we need a 3rd person perspective in order to determine one’s identity over time. (from P1, P2)
P4. The 3rd person perspective involves representing ourselves from the perspective of an external observer, i.e., from the perspective of another mind
C. Therefore, in order to establish our actual identity over time, we must be able to think of ourselves from the perspective of other minds. (from P3 and P4)
On Keller’s reconstruction, Kant is offering a kind of transcendental argument for the necessity of positing other minds. We assume that we are identical over time. In order for this to be possible, however, we cannot ground our identity over time by appealing to the 1st-person perspective alone. As Keller writes:
From the purely first-person perspective, there does not seem to be any way of drawing a distinction between one’s representation of one’s identity over time and one’s actual identity over time. In order to get a feel for this distinction, one must be able to shift from the first- to the second or to the third-person perspective. (1998: 176, emphasis added)
Akin to Wittgenstein’s private language argument, Keller suggests that other minds are necessary for distinguishing between what seems to be the case and what actually is the case. Interestingly, this seems to be the inverse of a view Kant defends in the 2nd Paralogism. As he writes there:
It is obvious that if one wants to represent a thinking being, one must put oneself in its place, and thus substitute one’s own subject for object one wants to consider…; and it is also obvious that we demand absolute unity for the subject of thought only because otherwise it could not be said: ‘I think’ (the manifold of representation) (A354).
Kant argues that in order to be able to represent other minds, we need to think about them from our 1st person perspective. That is, we must represent another person’s mind by putting ourselves in their place. As Keller puts it, “One must already put oneself in the position of another in order to ascribe consciousness to some other person.” By contrast, on Keller’s reading of the 3rd Paralogism, Kant defends the opposite claim. That is, in order to be able to represent ourselves as enduring over time, we need to think about ourselves from a 3rd person perspective, seeing ourselves as an ‘object’ represented by other minds. If it was impossible for us to take up this hypothetical perspective of another mind, we would never be able to draw the distinction between it seeming to us to be case and it actually being the case with respect to our own identity over time.
5. Faith Approach: Other Minds as a Moral Belief
So far we have discussed three different approaches that Kant takes to the problem of other minds. First, Kant provides a wholly negative answer to the problem in the Lectures on Metaphysics. Second, Kant offers an empirical argument in the 2nd Paralogism. It was argued there that we can infer from the behavior of others that they have minds. Third, on Keller’s reading, Kant offers a transcendental argument for the existence of other minds in the 3rd Paralogism. On this view, other minds are necessary for determining our own identity in time. One final strategy can be found in Kant’s writings about moral faith. In the “Canon of Pure Reason” of the 1st Critique, Kant defends the view that what he calls ‘belief’ or ‘faith’ (Glaube) does not require evidence in order for it to be rational. Because we cannot know other minds through inner or outer sense, Kant’s appeal to moral faith is important here. On this view, we don’t need to have evidence for other minds to be rationally justified in believing that they exist.
Kant speaks of ‘belief’ as one way of “assenting” or a way of holding something to be true. Kant describes assent as “an occurrence in our understanding that may rest on objective grounds, but that also requires subjective causes in the mind of him who judges [A656/B684].” That is, a person S who assents to some proposition P does so on the basis of some subjective or personal considerations and on some objective or evidential considerations. In this way, S takes her subjective and objective grounds to justify her assenting that P.
Now if S’s assent relies on these grounds, it follows naturally that judging whether S’s assent is rational or not depends on how good her objective and her subjective grounds are. Kant puts this in terms of “sufficiency.” Following Andrew Chignell, we can define “objectively sufficient” grounds as follows:
S has “objectively sufficient” grounds for assent that P = df. S would appeal to things such as arguments, experiences, or testimony that render the proposition she assents to highly probable in being true
For example, take my assent that “Boston is a city in Massachusetts.” I have objectively good grounds for this assent; I’ve been Boston and can testify that it falls within the borders of Massachusetts. What it means for someone to have “subjectively sufficient” grounds is a bit trickier. Chignell argues that there are two different senses in which a ground is “subjectively sufficient.” Intuitively, the first sense of subjective sufficiency is simply when a person takes themselves to have good evidence for their assent. We can formulate the first sense of ‘subjectively sufficient’ as follows:
S has “subjectively sufficient” grounds1=df. S has objectively sufficient grounds (or good evidence) for assenting that P and S would cite those grounds as the basis for that assent
The second sense of subjective sufficiency is when a person doesn’t have objectively sufficient evidence but does have certain practical grounds for her belief. We can formulate the second sense of subjective sufficiency as follows:
S has “subjectively sufficient” grounds2=df. S has subjectively sufficient grounds when S’s assent that P enables S to realize some interest, goal or end that S has
Therefore, S’s assent is rationally justified so long as she has “objectively sufficient” grounds and/or “subjectively sufficient” grounds. S’s assent is not rationally justified if her grounds are both “objectively insufficient” and “subjectively insufficient.”
All assents involve an objective and subjective component. However, these come in varying degrees of justification. As Kant famously argues, in the case of knowledge, we have both objectively sufficient and subjectively sufficient grounds for assent. In the case of opinion, we have both objectively insufficient and subjectively insufficient grounds for assent. Finally, in the case of belief or faith, we have objectively insufficient but subjectively sufficient grounds for assent. In keeping with this, Kant writes: “The word “belief”… concerns only the direction that an idea gives me… that holds me fast to it, even though I am not in a position to give an account of it from a speculative point of view [688].” Belief is assent to a proposition that gives us “direction”. However, beliefs don’t require us, as Kant puts it, to “give an account of it from a speculative point of view.” Instead they just require what Andrew Chignell helpfully calls a ‘non-epistemic merit’. He defines non-epistemic merits as “a property of an assent that makes it valuable or desirable for a particular subject to have given her goals, interests, and needs.” In fact, for some beliefs, we could never be in a position to cite objectively sufficient evidence. Paradigmatic examples of this sort of belief include God, immortality of the soul, and freedom, that is, ‘the Practical Postulates’.
These are cases of what Kant calls ‘moral belief’. To count as moral belief, assent must satisfy two conditions. Kant states both of these in his 1786 essay What Does it Mean to Orient Oneself in Thinking. The first is a negative claim which I will call the “No Evidence Condition” [NEC]. We can find this expressed in the following:
For if it has been previously made out that there can be no intuition of objects or anything of the kind… then there is nothing left for us to do except first to examine the concept with which we venture to go beyond all possible experience to see if it is free of contradiction, and then at least to bring the relation of the object to objects of experience under the pure concepts of the understanding – through which we do not render it sensible, but we do at least think of something supersensible in a way which is serviceable to the experiential use of our reason. For without this caution we would be unable to make any use at all of such concepts; instead of thinking, we would indulge in enthusiasm (8:139).
There are two features here. First, faith or belief can never contradict the available objective evidence (8:144). For example, I can’t rationally believe that there is a flying spaghetti monster in this room. This contradicts what my senses – and hopefully everybody else’s senses – tell them about this room. Second, faith or belief must have no supporting evidence, i.e., it can never be transformed into a claim of knowledge (8:141). For example, belief in the existence of God or in the immortality of the soul can never be empirically proven. The second feature is a positive claim that I will call the “Need of Practical Reason Condition” [NRC]. As Kant writes:
Far more important is the need of reason in its practical use, because it is unconditioned, and we are necessitated to presuppose the existence of God not only if we want to judge, but because we have to judge. For the pure practical use of reason consists in the precepts of the moral laws. They all lead, however, to the idea of the highest good possible in the world insofar as its possible only through freedom…Now reason needs to assume, for the sake of such a dependent highest good, a supreme intelligence as the highest independent good…in order to give objective reality to the concept of the highest good, i.e., to prevent it, along with morality, from being taken as a mere ideal, as it would be if that whose idea inseparably accompanies morality should not exist anywhere (8:139).
On Kant’s view, rational agents are subject the unconditional commands of morality. In keeping with this, human beings have an unconditional obligation to pursue moral ends that are “absolutely necessary”. One thing which morality commands is that we pursue the highest good. That is, the highest good is a necessary object of morality. As Kant writes:
[T]he promotion of the highest good, which contains this connection [between virtue and happiness] in its concept, is an a priori necessary object of our will and inseparably bound up with the moral law… (5:114)
In order to realize the highest good, we have to meet two conditions: first, complete moral perfection or “holiness of will” and second a state of happiness proportional to our moral character, that is, our “virtue”. If this highest good is a necessary object of moral willing, then we have to assume that it is possible. In the passage above, Kant argues that practical postulates like God and freedom are necessary conditions for the possibility of the highest good. First, we must presuppose that we have freedom to act as morality demands, that is, to autonomously fulfill our moral obligations. Second, we must presuppose that God exists in order to guarantee that happiness will be distributed in exact proportion to our virtue. Because God and freedom are necessary conditions for the highest good, to deny either would necessarily make morality a “mere ideal”. For in this case, morality would demand something – namely, the highest good – that isn’t possible to realize. Since we are committed to morality, and since morality insists that the highest good is a necessary object of our moral willing, Kant concludes that we must have moral belief in these practical postulates.
Recall that beliefs can be justified if they have what Chignell calls non-epistemic merits, that is, they enable us to realize some interest, goal, or end that we have. This is what we called “subjectively sufficient grounds” in the second sense. We saw above that the belief in God and freedom have such subjectively sufficient grounds. Though we are never in a position to know that God exists or that we are free, we must believe both, since assent to these propositions is necessary for morality. Here we return to the question of whether the existence of other minds fits the bill for moral belief. Carol von Kirk argues that it does. She argues that we have to assume other minds exist because otherwise, we cannot make our interactions with other people fully intelligible. In particular, other people display moral behavior. As she writes:
When we consider people the only way of making sense of all of their actions is to assume that, in addition to being subject to the natural causal order, they are also subject to an order based upon self-awareness… For Kant, rationality is not something that is inferred from “the data” because there are no data regarding the moral realm unless rationality is presupposed. Rationality must be assumed at the outset if a particular type of behavior is to be coherent (1980: 54)
So in order to have a coherent understanding of the behavior of others, we must conclude that other minds exist. For such reasons, Kirk argues that there is no problem of other minds for Kant. I want to make a stronger claim here. In contrast to Kirk, my claim is that other minds are necessary for morality in a way very similar to the Practical Postulates. Recall that Practical Postulates like freedom and God are necessary in order to realize the highest good. The highest good is a necessary object of moral willing. Therefore, we must presuppose such practical postulates – which makes the highest good possible –if morality is not to be, as Kant puts it in the 2nd Critique, “fantastic and directed to empty imaginary ends and… therefore in itself false” (5:114). In a parallel way, my claim is that other minds are equally necessary conditions for moral action. Morality imposes on us various duties and obligations towards others. In order for it to be even possible for us to carry out such moral duties, other rational agents would obviously have to exist. So while Kirk argues that we must believe in other minds in order to make sense of other people’s moral behavior, I argue that other minds are necessary for the possibility of moral actions themselves.
6. Conclusion
What should we think about these four different approaches? Do any of them succeed? In conclusion, I discuss the pros and cons of each view. First, in terms of the skeptical approach, I think that Kant is correct in insisting that other minds can never be an object of cognition for us, either for inner sense or outer sense. What seems dissatisfying about this approach, however, is that instead of refuting skepticism, it essentially accepts the skeptical conclusion raised by the problem of other minds.
Second, in terms of the empirical approach, I think that Kant’s brief remarks in the 2nd paralogism are significant insofar as they anticipate Mill’s celebrated argument from analogy by appealing to ‘signs appearance’. The problem with Mill’s approach is that it seems doxastically irresponsible. It generalizes from one individual case, namely, my own, to all other persons. By contrast, the problem with Kant’s approach is that he seems to simply take it for granted that we can directly causally infer that other minds are the causes of signs in appearence. However, this is far from a satisfactory reply for somebody who doubts the existence of other minds in the first place.
Third, in terms of the transcendental approach, what seems good about it is that, if successful, it is arguably the strongest of all four views discussed here. It makes the existence of other minds necessary for the possibility of self-knowledge, in particular, for knowledge of ourselves as identical over time. In this way, objective self-knowledge entails belief in other minds. This argument, however, faces a serious problem. In the end, it doesn’t seem to prove that other minds actually exist. All that it establishes is that we have adopt a hypothetical 3rd person perspective in order to regard ourselves as enduring over time, regardless of whether anybody occupies this perspective or not.
Fourth and lastly, in terms of the faith approach, what seems good about this strategy is that it is more modest than the others views because it doesn’t claim that we can theoretically know that other minds exist. If successful, it establishes that we are at least rationally justified in believing that other minds exist. However, this argument has its problems too. First, it assumes that we accept the existence of morality and in particular, that we have genuine moral duties to others. Consequently, if a skeptic were to deny morality, this argument would fail to address their worries. Second, the argument is too weak. We are not content with having mere faith about the existence of the external world. So why should we be content with mere faith about the existence of external minds? In the end, I think that Kant fails to adequately resolve skeptical worries about the existence of other finite minds. At best, Kant can establish that their existence is a tenet of moral faith, and never something we can truly know.
A Humanities Symposium 