Written by,
Yap Xiao Wei
Edited by,
Joshua Chua (Editor 20/21’)
Kang Sheng & Celine (Language Editors 20/21′)
In this paper, I will argue that essential assumptions behind Descartes’ metaphysical concepts are – despite the claim that those concepts are based on a priori knowledge – dependent on a posteriori knowledge. In doing so, I will attempt to explain the origins of some assumptions using Hume’s ‘copy principle’ – showing that Hume, an empiricist, better explains the nature and origins of metaphysical concepts (mainly that, unlike Descartes claims, they can only be conceived a posteriori).
To start, I will explain Hume’s ‘copy principle’, as well as his view on the origins of metaphysical concepts [Section 1]. I will then explain Descartes’ motivations towards, and views on, the origins of metaphysical concepts [Section 2]. Next, I will uncover some underlying assumptions made to reach these concepts and show how these assumptions are based on knowledge or ideas he could only have obtained or ‘copied’ through experience (or, as Hume calls it, ‘impressions’) [Section 3]. In effect, this will show that Descartes’ metaphysical claims are fundamentally impossible to make without empirical knowledge outside the mind, leading to a contradiction in his rationalist philosophical beliefs. Finally, I will consider and respond to a possible objection to my argument [Section 4].
Section 1: Hume
Hume’s ‘copy principle’ states that products of the mind are entirely dependent on impressions; we passively take in vivid elements of the world around us through sense perceptions and make duller ‘copies’ of these elements in our minds. Further products of the mind – actively put together by the imagination – are the augmentations and/or combinations of these copies. For example, the idea of the mythical Pegasus comes from combining the ideas of “horse” and “wings of a bird”, with said wings augmented in-mind to be large enough to allow the horse to fly. To Hume, God is simply a more extreme example, with impressions of virtue, power, and knowledge augmented to infinity. That said, Hume’s stance is that anything the mind can conjure – no matter how fantastic in theory – possesses less impact or strength than even the weakest impression. That is to say, the idea of God – which rationalists like Descartes, Spinoza, and Leibniz refer to as the highest being – is weaker than anything we can experience through our senses.
This informs Hume’s view on metaphysical concepts: as they are constructed merely in our minds and have no form through which our sense perceptions can receive them, they are little more than amalgamations of dull concepts based on impressions. Consequently, they cannot have any truth-bearing value in themselves. Any conclusion drawn through only “pure reason in the mind” is, in effect, purely conjectural as there is no possible way of verifying if it actually holds any truth. Hume adds that metaphysical concepts are obscure and unreliable due to the presence of dogmas in the world affecting the common person. Dogmas lead them to form mistaken conclusions based on arbitrary ideas that they are convinced are true – specifically, superstitions like the widespread belief in God’s existence at the time. Rationalist philosophers like Descartes rely significantly on the existence of God to support their metaphysical concepts, which is one reason Hume disagrees with them.
As Hume argues that metaphysical concepts are dependent on impressions, it follows that arguments formed using such concepts are a posteriori and not a priori. Instead, they are dependent on experiential knowledge. Hence, Hume argues that metaphysical arguments (that claim to obtain truth with certainty) can never be certain, as experiential knowledge is contingent and not absolute.
Another key difference that arises from this and distinguishes Hume’s beliefs from those of rationalist philosophers is that he does not consider sense experiences to be obstacles in the search for knowledge and truth. Instead, he considers sense experiences as valid means of obtaining knowledge.
Section 2: Descartes
Descartes begins his Meditations with the goal of finding something he can reliably base knowledge on. This is important to him because experience has shown that sense perceptions are sometimes wrong (notably when it comes to dreams or hallucinations). If an apparatus used to measure something is wrong multiple times, then it is somewhat unreliable and its findings should be regarded with scepticism. In Descartes’ case, the senses are used to receive and “measure” knowledge from the world around us. To find his “stable and reliable” starting point for knowledge free from prior and future “mismeasurements”, his first step is to assume that everything he perceives and knows about the world beforehand must be false. In order to better force himself to purge his beliefs, he posits that they are the result of him being deceived by an Evil Demon.
From this blank slate where nothing he knows is true, he proceeds to conclude that the first thing he can be sure of is the fact that he is thinking; to quote, a thinking thing. This premise leads Descartes to demonstrate subsequent conclusions on concepts like material bodies (extension), God, reality, and overall truths. In essence, these metaphysical concepts are reliable because they originate almost purely from reason as a thinking thing. Thus, he claims that such concepts are undeniably true, with minimal or no reliance on sense perceptions (which may be wrong) and, by extension, empirical knowledge.
Section 3: Descartes’ Empirical Assumptions
For Descartes, the metaphysical fact that the individual is a thinking thing forms the basis of all his further metaphysical concepts of reality, necessity, and God. However, while the conclusions he draws afterwards mostly rely on this first fact and not empirical knowledge (thus seeming a priori), the assumptions that lead towards the “first step” stand out as clearly reliant on empirical knowledge. They are, among others: that he is a singular thing; that he could be deceived (by an Evil Demon, in order to purge misassumptions in his methodology in Meditations); and that he can be mistaken.
Hume’s ‘copy principle’ explains how these assumptions are a posteriori: The concept of the ‘self’ or ‘singular thing’ comes from the interaction between the individual and other individuals. As such, Descartes’ certainty that he is a ‘singular thing’, and not ‘a collection of things’ or ‘multiple thoughts working together’, is through sense perception of other organisms and structures in relation to himself in the world. Through these interactions, he senses that he is a singular thing as opposed to a collection, by perceiving differences subtle or significant between himself and everything else. However, if he were to truly purge himself of all empirically obtained knowledge and assumptions, there would be no reason to think that he was a ‘singular thing’, either.
The concept of deception is also one that is known through experience. Were Descartes something that did not experience interactions with other individuals, he would not have observed a tendency to deceive others. This can be understood through the fact that a child might accept all knowledge provided to them as truth until they have had multiple encounters with falsehoods and deviations from “what actually is”. Until then, there would be no reason for the child to think that deceit existed. Another way that one learns the concept of deception is through deceiving others – which also relies on experience. This implies that one cannot be said to be arriving at an a priori truth through the reliance on the empirically obtained concept of deception or doubt. Additionally, there is no a priori basis from which to think that deception exists as this inference also relies on empirical knowledge. Thus, Descartes’ radical scepticism is reliant on empirical beliefs.
The concept of mistakes, as with deceptions, comes from a conception of “rights and wrongs” – or veridicality. Similarly, the only way one can know of rights and wrongs is through experience. If there are no standards to abide by or no way for one to encounter situations in which they (or someone else) can make mistakes with tangible repercussions, then there is no basis to consider anything as a mistake. As such standards originate from experience, veridicality is reliant on experience. Mistakes, after all, are characterised by some form of loss or missed gain – which require impressions of things that can be lost or gained, making mistakes unfavourable. As with deception, these concepts are not a priori.
These arguments show that the very basis of Descartes’ metaphysical concepts/arguments are largely reliant on empirical knowledge, as Hume posits (against rationalist philosophers in general).
Section 4: Is this a fair criticism?
One possible objection against my overall point is that it unjustly demands too much of metaphysical concepts – that it is unreasonable to expect that all metaphysical concepts need to be purely a priori. In effect, this would mean conceding that the formation of basic ideas is indeed reliant on concepts only attainable through experience. For how else would one come to know of virtue, deception, failure, and individuality without sense perception interactions with the material world? Regardless of this concession, the most important part of Descartes’ initial metaphysical discovery is the arrival at the certain conclusion that he is thinking, which he concludes without prior empirical knowledge.
My response to that claim is that it understates the severity and reach of the initial empirical assumptions Descartes makes. Descartes does not simply conclude that he thinks; it is through methodical denial of prior knowledge and the seeking of an unshakeable fact that he arrives at the concept of a thinking thing, and his specific aim is to establish a foundation from which he can base future knowledge free from unreliable elements. To establish said foundation while relying on the unreliable sense perceptions he seeks to avoid is an ironic endeavour, and even if this does not completely nullify Descartes’ concept of a thinking thing, the unshakeable a priori foundation he intends to set up is clearly untenable.
The metaphysical concepts that Descartes relies on are therefore still subject to empirical knowledge and, as Hume claims, are not where one can find “necessary truths”. Consequently, metaphysical argumentation is not free from sense perception: even the mind’s reason is necessarily subject to the empirical.
Editor’s Note:
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