This essay outlines David Hume’s empiricism and bundle theory of the self and assesses in what ways can the latter be considered defensible. Hume’s empiricism is a radical form of scepticism that grounds all knowledge in experience. His bundle theory is a view of the self that follows as a necessary consequence of that scepticism. The concept of the self takes on many different forms in various religious traditions and philosophies. According to Hume, no belief in a particular concept of the self is justified when there is no direct impression of the conceptualised self as an object of experience. All the self amounts to in Hume’s view, is the continual flux of experiences united only by the natural relations of association of the mind. The view of a unified self that goes beyond this is, according to Hume, a fiction produced by the imagination. Hume’s bundle theory is defensible only within the empirical system Hume develops. In the broader picture of epistemology, bundle theory is defeated by the work of Kant who expands the boundaries of Hume’s empiricism to include knowledge of the necessary conditions of experience. In doing so, Kant adds additional synthetic a priori knowledge about the unity of experience that renders the bundle theory of the self obsolete.
Empiricism emerged in force as a successful epistemological doctrine from the tradition known today as the British empiricism. Prior to this, empiricism appeared as a common general attitude rather than a comprehensive system. This attitude can be seen in the following sentiment from the pre-socratic philosopher Heraclitus: “the things of which there is sight, hearing, experience, these I prefer” (Hankinson 2018). While not explicitly empirical, this sentiment does contain the spirit of empiricism. Aristotle offered a more methodological empiricism. He regarded the senses as reliable and believed they play a necessary role in the acquisition and development of knowledge. Things as they appear to the senses (ta phainomena), provide both the starting point for inquiry, and a guide for the success of inquiry. Aristotle’s use of ta phainomena goes beyond what later empiricists such as Hume would consider experience as it also includes reputable opinions. This makes it difficult to categorise Aristotle as an empiricist in the way the term is understood today. Instead, Aristotle can be understood as a genetic empiricist through which modern empiricists can trace their lineage to.
It was not until the early modern period that empiricism emerged as a systematic philosophical tradition. Locke marks the true beginning of that tradition. Locke produced the first polished theory of the mind grounded by the principle that all ideas originate from experience. He rejected the view that innate ideas exist and instead described the mind at birth as a blank slate. His aim was to demonstrate how experience alone can provide a coherent understanding of the world. He used his empiricism to challenge much of the rationalist metaphysics that were popular throughout the early-modern period. He rejected the cartesian notion that knowledge of a substantial self can be acquired through thinking alone and instead grounded the self within the continuity of personal identity over time (Gordon-Roth 2019). Hume adopted Locke’s starting point that all ideas have their origin in past experiences but radicalises it by relentlessly pushing it to logical conclusion. In doing so, he produced an extreme skepticism which not only undermines rationalist metaphysics, but also many of the conclusions that Locke’s version of empiricism appeared to support. Most notably, Locke’s view on personal identity.
The so-called copy principle can be considered to be the first principle in Hume’s empirical system and provides a good launching pad for discussing Hume’s system. Quoting directly from book one of Hume’s A Treatise on Human Nature, the copy principle is the rule “that all our simple ideas in their first appearance are deriv’d from simple impressions, which are correspondent to them, and which they exactly represent” (Hume 1739–40, 1.1.1). Hume uses the terms impressions and ideas to denote what he considers to be the distinctions to which all human experiences can be categorised. The kind of experiences that strike us forcefully with vividness and clarity Hume names impressions. Within the impression distinction, the qualities of objects that come to experience through the senses can be included. The visual quality of green, the bitter smell of coffee or the hardness of a solid wooden desk all represent simple impressions when they are forced upon experience independently of choice or will. Impressions can also come from what Hume calls reflection. These are impressions that arise from within the mind or body that strike experience with a similar degree of force as the impressions of sensation. Perceptions such as emotions, desires or pain can all be classed as impressions of reflection. After an impression has been sprung upon experience, a faint copy of its particular quality is created which can then be recalled by memory and used in thinking and imagination. Experiences of this kind are what Hume called ideas.
The copy principle only applies to what Hume distinguishes as simple impressions and simple ideas. An impression or idea is said to be simple if it cannot be divided into smaller components. When presented with the impression of a particular shade of green, there is no possible further division that can be made without destroying the precise quality that constitutes the impression itself. Similarly, the sound of a single particular tone cannot be broken down without losing the distinctive character of that auditory impression. In Hume’s system, these simple impressions and their corresponding simple ideas, each with their precise and unique character, can be thought of as the indivisible units that constitute experience. In the copy principle, Hume is expressing that all of our simple ideas derive from the simple impressions acquired through sensation and reflection which they represent.The copy principle establishes Hume’s view of the absolute dependence the mind has on its prior experiences. The only ideas the mind has access to for thinking or imagining are those that have been derived from experiences that have in the past been impressed upon it through sensation or reflection.
Impressions are typically not presented to experience in their simple form, but as complex clusters of qualities which the mind interprets to be a single complex entity. When looking at a pencil, its distinct sensory qualities of colour, shape, size and texture are all presented together as one item of perception. Although complex impressions are passively received as a conglomerate, they can be analysed and deconstructed into a collection of individual simple impressions. Each of which gives rise to a corresponding simple idea. Like impressions, the distinction of complex is also applied to ideas. The origin of complex ideas differs from that of complex impressions. While complex impressions are provided through sensation, the mind constructs complex ideas from simple ones by arranging and ordering them using what Hume calls principles of association. He identified three kinds of relations the mind uses to do this: resemblance, contiguity and causation (Hume 1739–40, 1.1.4).
When one idea naturally leads the mind to another because the two share similar qualities, Hume would say that the ideas are related through resemblance. When listening to a song of a particular genre, the mind may immediately call to mind other songs of the same genre because of certain defining sounds or musical themes that are associated with that particular musical style.
When we are exposed to a new idea, its resemblance to ideas already grasped by the mind naturally causes the mind to relate it accordingly. Resemblance is not a relation occurring between real things in the world, it is a cognitive function the mind uses to quickly move between similar ideas.
Contiguity is the association principle that connects perceptions based on their proximity in time and space. A relation of contiguity occurs when the perception of one object naturally calls to mind other objects located nearby. These associated perceptions can be taken together as a single complex idea. For example, a large room on a university campus filled with labelled books arranged in the same space is experienced as a library. The close conjunction of these perceptions leads the mind to associate them as a new complex idea rather than as a mere collection of individual perceptions.
The last of the three associations of ideas Hume identifies is causation. This relation occurs when the mind and imagination naturally relate ideas where one is expected to follow another. After getting caught in a rain storm and becoming wet, the mind naturally frames the idea of being caught in the rain as the cause of getting wet. Similarly, If a person drops a glass drinking cup onto a tiled floor and it smashes, an observer might say that the act of dropping the glass has caused it to smash. The relation of causality in both of these cases comes from the habitual expectation that one event regularly follows another. Crucially, Hume points out that the causal relationship only exists as an association of ideas in the mind despite the popular interpretation that causality is a necessary and real phenomenon in the external world. Hume argues that this belief in real world causal necessity comes from a projection of causality as an association of ideas onto objects in the external world. There is no real relationship beyond the basic conjunction of one event following another.
In summary, Hume’s empirical foundation emerges from the notion that all knowledge comes from experience. Experiences can be categorised into two distinctions. There are impressions which are the vivid and lively experiences provided by sensations and impressions. From impressions, the mind forms ideas which are faint copies of impressions used in thinking and imagination. Every simple idea the mind forms always comes from a simple impression. Finally, the mind forms complex ideas according to the three associations of ideas: resemblance, contiguity and causation. In Hume’s philosophy, the validity of ideas depends on how they originate within this foundation. Hume’s system grounds knowledge in observations supported by empirical evidence. The modern scientific method is distinctly Humean as it reaches its conclusion through rigorous processes such as experimentation and methodically eliminates hidden assumptions not grounded in observation. Ideas produced by means of intuition or associations of relation are not valid. Hume’s empiricism can be understood as a radical form of scepticism, and he uses it to destroy many of the popular philosophical ideas which were confidently held at the time including ideas pertaining to the self.
In the early modern period, discussions about the self were central to some of the key philosophers of the time, but these conceptions, and the arguments used to justify them are untenable within Hume’s system. Descartes, like Hume, founded his philosophy on a radical scepticism. Hume’s system is grounded in the principle that all knowledge originates in experience, whereas Descartes’ scepticism extends even to experiences themselves and to the sensory faculties that generate them. By applying his method of radical, systematic doubt, Descartes argues that every belief about the external world, the body, and even mathematics could be mistaken. The certainty that he is thinking is the only piece of knowledge that survives this radical doubt. Even if all of his experiences were the product of an elaborate deception by a powerful God-like being, he could still be certain that he thinks, and therefore he exists (Nelson 2007). For Descartes, this is a satisfactory justification that the self exists. Hume however, disagrees. When Hume introspects, he does not perceive an enduring self, instead, all he encounters is a constant flux of perceptions. As he thinks and moves his eyes around, impressions appear and disappear. No matter where in experience he looks, he never experiences an impression of the self. Since, on Hume’s copy principle, all ideas come from impressions, and there are no impressions of the self, there is no way to empirically justify the cartesian picture of the self.
Lockean personal identity also posits a notion of the self which is unacceptable in Hume’s empiricism. For Locke, a person is united by the continuity of their experience over a lifetime. He ties the notion of the self to the persistence of a single diachronic subject, where the unification of cognitive faculties such as thought, reflection and memory into a single stream of consciousness connects an individual’s past and present into one consistent and stable being in time (Gordon-Roth 2019). Hume argues that Locke’s assertion that these cognitive faculties considered together can be considered a singular entity is an error. Hume instead claims that the separate faculties represent a diversity of separate entities, and unifying them into a singular concept of the self is a fiction produced by the imagination. What is really occurring in Locke’s view according to Hume is mistakenly ascribing the idea of sameness to what is nothing more than a collection of diverse impressions with no necessary unifying connection (Hume 1739–40, 1.4.6).
In Hume’s empiricism, the notion of the self is confined only to the experience of a bundle of unconnected perceptions.The notion of a self that binds these perceptions together into the concept of a self comes only from the mind’s natural tendency to associate ideas. A habitual custom that does not amount to any ontologically valid existence outside of imagination. The question of whether or not this theory of the self is defensible depends entirely on what is meant by defensible. It is certainly defensible within Hume’s empirical foundation, as Hume has successfully shown that there are no impressions of the self, and since all knowledge comes from experience alone, there are no other valid means for positing a self independently of a mere bundle of perceptions.
Despite the defensibility of Hume’s bundle theory in a strictly empirical sense, it is deeply unsatisfying. Generally, common intuitive beliefs in the self can be empirically reduced to customs used by the imagination, but in doing so, there is a sense that there is some crucial aspect of selfhood that has been left out. Hume himself was disturbed by this, in the appendix of book one part four, Hume expresses that while he is content in the epistemic rigor he applies to his philosophy, he is uneasy about his empiricism’s inability to offer a coherent account of how these experiences are unified a single enduring consciousness (Hume 1739–40, 1.4.7). This lack of unity of experiences is a serious dilemma for Hume’s bundle theory, and one that makes it difficult to endorse its overall defensibility. This dilemma would be resolved by the next great work in the canon of epistemology: Immanuel Kant’s transcendental idealism.
Kant agreed with Hume’s conclusion that many of the rationalist views such as necessary causal connection and concepts of the self as a substance formulated using pure reason cannot be justified as metaphysical truths, but he argued that in analysing the necessary conditions that presuppose experience, we can access a new kind of knowledge. In order for experience to exist in the first place, there are certain conditions which must be met to make this possible. Without these conditions, experience itself could not exist. By analysing these conditions, we can deduce what Kant calls synthetic a priori knowledge (Grier n.d.). For Hume, a priori knowledge is limited to relations of ideas which are true by definition and independent of experience, but is incapable of producing new knowledge not already contained in an antecedent. Like a priori knowledge, synthetic a priori knowledge is gained independently of the objects of experience, but it reveals new knowledge in the form of the necessary conditions of that experience. Synthetic a priori knowledge is thus a tremendous innovation by Kant, and it pushes the boundaries of what can be known beyond the Humean picture.
Kant’s transcendental idealism maintained experience as the ultimate boundary of what can be known. He divided reality into two domains: the realm of appearances, which he called the phenomenal, and the realm of things in themselves, or noumena. Since noumena lie beyond the limits of experience, Kant maintained that they are completely unknowable. By analysing the objects of the phenomenal realm, and the necessary synthetic a priori conditions that make those experiences possible, some of the concepts lost to Hume’s scepticism are regrounded. In Hume’s empiricism, it is impossible to gain knowledge of necessary connections such as those supposed in the idea of causality, as all knowledge comes from impressions and experience reveals only a constant conjunction of events, not any necessary connection between them. In Kant’s transcendental idealism, however, knowledge of causality can be acquired by understanding it as a necessary condition that brings about the flow of sequential events as they are experienced. When we experience events occurring in the world, we experience them as having a determinate temporal order. Kant argues that in order for this to be possible, the mind contributes causality as the principle governing this temporal ordering. In this sense, causality must exist as it makes experience of ordered events possible. This is still a far-cry from the archaic notion of perfect metaphysical causality of the rationalist tradition but it is a valid concept of causality whilst still maintaining the standard of strict epistemic rigor of Hume.
Kant also agrees with Hume that we cannot have knowledge of a substantial self because such a self never appears within experience. However, Kant rejects Hume’s conclusion that nothing more can be said about the self. By understanding the necessary conditions of experience, we can gain synthetic a priori knowledge of a unity of apperception. In other words, we can deduce knowledge of a necessary unity that binds experiences together into a single unified stream of consciousness. When we have thoughts and experiences, we are always aware that they are exclusively our own, and we ascribe the same thinking subject to them. Since we can distinguish our own thoughts and experiences from the objects we experience, experience itself must presuppose a unifying self-conscious standpoint under which those experiences are unified. Crucially, this unifying self-consciousness is not an object, or a thing in the world. It is a necessary condition that presupposes experience. In understanding the unity of apperception as a synthetic a priori deduction and not as an empirical observation, Kant provides a more detailed outline of the self without contradicting Hume and without reaching beyond what experience permits him to posit. Using only Hume’s empiricism, we are forced to accept that the self is nothing more than a bundle of perceptions. With Kant, the conclusion changes to the slightly more optimistic view that there must be an underlying unifying stand-point from which experiences are perceived. We could say that Kant’s view expresses that there must be a self, not as a thing-in-itself but as a necessary condition of experience.
In expanding the boundaries of knowledge from the confines of experiences themselves to include synthetic a priori deductions, he successfully liberates the idea of the self from a mere bundle of perceptions to a necessary condition of experience. Because of this success, Hume’s bundle theory cannot be said to be defensible. Rather than seeing Hume’s empiricism and consequential bundle theory as the final word on the matter of the self, his work can be better interpreted as a great clearing-away of faulty reasoning and unsubstantiated ideas about the self and bringing discussions back to a more sober and grounded position. Ironically, Hume and Kant’s rigorous epistemology creates a problem for further understanding of the self. Both Kant and Hume agree that the self cannot be known as an object. This is perhaps due to the fact that whatever the self is, it cannot be known in the absolute sense of the word. If the self cannot be known, then no rigorous epistemology that seeks to ground all beliefs in knowledge can ever be capable of understanding it. Hume famously destroyed the tradition of early modern rationalism, but in order to understand the self in the wake of this destruction, it might take the pure reason and free creativity of rationalism to do it.
Bibliography:
Bennett, Jonathan. “David Hume.” Early Modern Texts. https://www.earlymoderntexts.com/authors/hume
Grier, Michelle. n.d. “Kant: View of the Mind and Consciousness.” Internet Encyclopedia of Philosophy. https://iep.utm.edu/kantview/
Gordon-Roth, Jessica. 2019. “Locke on Personal Identity.” Stanford Encyclopedia of Philosophy, edited by Edward N. Zalta, Winter 2025 Edition. https://plato.stanford.edu/entries/locke-personal-identity/
Hankinson, R. J. 2018. “Empiricism in Ancient and Medieval Philosophy.” Stanford Encyclopedia of Philosophy, edited by Edward N. Zalta. https://plato.stanford.edu/entries/empiricism-ancient-medieval/
Nelson, Alan. 2007. “Descartes’ Epistemology.” Stanford Encyclopedia of Philosophy, edited by Edward N. Zalta. https://plato.stanford.edu/entries/descartes-epistemology/