How Can We Know That We Know? Descartes on Clear and Distinct Perception

In this paper, I will be discussing Descartes’s idea of clear and distinct perception in various ways, beginning with his explanation of what it means for a perception to be clear and distinct and why this is important to him. This explanation will lead to a further explanation of Descartes’s faith in clear and distinct perceptions and the question of whether this faith is warranted. I will be making reference to Descartes’s writings as they appear in Cottingham, Stoothoff, and Murdoch’s (CSM) translation in The Philosophical Writings of Descartes, Volume II (II) and as they appear in the Project Gutenberg (PG) web version of The Principles of Philosophy (PP).

First, it behooves us to clarify the subject at hand and the reasons Descartes considered clear and distinct perceptions important. In the Principles, he states that “a great many persons. . .never perceive anything in a way necessary for judging of it properly” since “the knowledge upon which we can establish a certain and indubitable judgment must be not only clear, but also, distinct” (PG PP XLV). He further states that clearness consists in being “present and manifest to the mind” and that distinctness consists in being “so precise and different from all other objects as to comprehend in itself only what is clear” (PG PP XLV).

In the section that follows, Descartes explains that some perceptions (such as pain) can be clear, but not distinct. However, perceptions can never be distinct without being clear. So since a clear perception like pain is experienced by almost everyone, distinctness seems to be the rare differentiating feature of proper perception, which is the necessary foundation of proper judgment. For Descartes, this property of distinctness is inhibited by prejudices acquired early in life – “in our early years, the mind was so immersed in the body, that, although it perceived many things with sufficient clearness, it yet knew nothing distinctly. . .numerous prejudices were thus contracted, which, by the majority, are never laid aside” (PG PP XLVI-XLVII).

This means that Descartes believes that a juvenile habit of prejudicially perceiving things is carried throughout life by most people. It follows that because of this, they make judgments of perceptions which are present and manifest to their mind (clear) without being able to truly understand what any given notion is in-itself (distinct). This is to say that epistemic baggage clouds ordinary judgments to such a degree that it is difficult to know which are true or false, and to what degree they are such. With this in mind, it is easy to see why Descartes, as he sought to overcome skepticism and establish an ultimate foundation of scientific knowledge, emphasized clear and distinct perceptions (CSM II 9).

Early in the third meditation, Descartes gives an example of a very clear and distinct perception – the first that he presents:

“I am certain that I am a thinking thing.  Do I not therefore also know what is required for my being certain about anything?  In this first item of knowledge there is simply a clear and distinct perception of what I am asserting; this would not be enough to make me certain of the truth of the matter if it could ever turn out that something which I perceived with such clarity and distinctness was false.  So I now seem able to lay it down as a general rule that whatever I perceive very clearly and distinctly is true.” (CSM II 24, emphasis added)

From this excerpt we can learn several things about clear and distinct perceptions. By his use of “simply”, we learn that the cogito is supposed to be in a sense self-evident. It is present and manifest to his mind that he is thinking whenever he thinks, and because the perception of his own thought is epistemically simple it depends on nothing else for its explanation – in this way it is truly distinct.

By his use of words like “such” and “very”, we see that he wishes to emphasize how perceptions can be clear and distinct to varying degrees. Having established what he means by “clear and distinct”, this makes sense intuitively. It is obvious that these properties of clarity and distinctness may generally ebb for a plurality of reasons. Memories, for example, become less vivid and differentiated due to the passage of time. But perceptions like those which inform the cogito are immutably clear and distinct to the highest degree so long as we apprehend them, whenever we apprehend them.

Descartes seems to be claiming, and I am inclined to agree, that if he cannot be certain of any judgment or proposition which is based on perceptions as clear and distinct as those which inform the cogito, then certainty as a concept is farcical. This explains both why he cannot reasonably doubt what he clearly and distinctly perceives and why he thinks he cannot go wrong if he only accepts as true what he clearly and distinctly perceives – at least with respect to propositions or judgments which are based on perceptions as clear and distinct as those which inform the cogito and the cogito itself.

The issue, however, is that we cannot maintain this doubt-surpassing clarity in all of our perceptions at all times. So we cannot be sure that we have not erred in our judgment as soon as we “let go” of any particular perception, even if we remember having had a clear and distinct perception. Descartes attempts to solve this problem by arguing that God has placed the faculty of judgment in us, and that since God is perfect and thereby not a deceiver, God would not place a faculty of judgment within us such that, properly utilized (with regard to clear and distinct perceptions), it could lead us astray (CSM II 37-38). It is because of God, then, that our judgments based on clear and distinct perceptions are always accurate if we use this mental faculty correctly.

Here one may raise the objection of circular reasoning. If it is accurate to say that Descartes claims he can trust his clear and distinct perceptions only because God exists, but that God must exist because Descartes clearly and distinctly perceives that God exists, it seems Descartes would clearly be guilty of circular reasoning. At the end of the fifth meditation, Descartes says that he saw “plainly that the certainty and truth of all knowledge depends uniquely on my awareness of the true God” (CSM II 49). So the accusation of circular reasoning is potentially very dangerous for the entire system that Descartes has built in the meditations.

Arnauld raises something similar to this concern in the fourth set of objections, and Descartes’s answer is on its face quite simple. He points out that there is a distinction between “what we in fact perceive clearly and what we remember having perceived clearly on a previous occasion” and then argues that “we are sure that God exists because we attend to the arguments which prove this; but subsequently it is enough for us to remember that we perceived something clearly in order for us to be certain that it is true” (CSM II 171). This means that if his arguments for the existence and nature of God work, then at the time that Descartes is apprehending the clear and distinct perception of God’s existence, God’s perfect nature as that which guarantees the continued truth of Descartes’s clear and distinct perceptions becomes apparent. It is thereafter adequate to remember the truth of this conclusion in order to be aware of the guarantee that clear and distinct perceptions are true at all times. This seems to me to be a persuasive avenue of argument if we accept Descartes’s arguments for the existence and nature of God which quite reasonable in its addressing of the circularity accusation.

However, we are by no means obligated to accept these arguments as presented; we have only granted his premises in charitability to the text, to get a full and accurate picture of his beliefs. We may now make a number of objections to his arguments for the existence, function, and nature of God, as well as, to begin with, his notions of perception, sensation, temporality, and infinitude/indefinitude.

Or rather, we could – but that task is best left to another paper. In this paper, I have endeavored specifically to explore Descartes’s notion of clear and distinct perceptions. I examined what the term meant and why it was important to Descartes in order to show why he thought he could not doubt these perceptions and why he believed they would not lead him astray. I also explored, in brief, the problem of circular reasoning in his argument for the truth of clear and distinct perceptions, his rebuttal, and the apparent efficacy of this rebuttal.

The will to deceive supposedly stems from malice or wickedness; it is the result of a privation (in man) of some perfection which is by definition fully present in God. (CSM II 37)


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