Descartes: Method, Certainty, and Radical Doubt
Descartes’ Quest for Certainty
Descartes’ Four Rules for True Knowledge
Descartes proceeds to develop a method with rules designed to ensure that nothing false is accepted as true. He formulated four rules summarizing his analysis and reflections on the mathematical method and its applicability to philosophy.
Rule 1: The Rule of Evidence
This rule has two important elements. First, one must avoid precipitation and prevention. Precipitation is accepting as obvious that which is confusing and obscure. Prevention is not accepting as obvious that which is clear and distinct. Both lead to error, not due to reason itself, but due to the will, which may accept as true propositions over which absolute certainty has not been established. Secondly, this rule clearly establishes the necessity of clear (nitida) and distinct knowledge as characteristics of simple ideas obtained through intuition.
Rule 2: The Rule of Analysis
This rule proposes the systematic analysis of problems, breaking them down into simpler, clear, and distinct ideas.
Rule 3: The Rule of Synthesis
This rule outlines the process of synthesis, where deduction plays a key role. The sequence of the second and third rules follows the natural order of deduction. It builds upon simple natures to reach relative knowledge that cannot be obtained directly by intuition.
Rule 4: The Rule of Enumeration
This precept involves the complete enumeration and review of both the analysis and the synthesis. The purpose of these enumerations is to extend the certainty of intuition to the entire chain of deductions. This method is suitable only for reason and its natural way of knowing. Descartes’s goal is to find absolutely certain truth, about which no logical doubt is possible. He seeks self-evident truths that can serve as a permanent foundation for building a knowledge base with true, absolute guarantees. The initial problem is finding these truths, which is why the method is developed.
The Principle of Methodical Doubt
The first step in applying this method is to doubt everything previously believed and to reject anything about which there is even the slightest hesitation. The very act of doubting is a sufficient reason to provisionally reject a view previously considered true and to hold it in suspense until its validity can be established by reason. This initial step is called methodical doubt. This doubt must be considered methodical—a tool to achieve clear and distinct ideas through intuition. Descartes presented three main reasons for such doubt:
Reason 1: Deceptive Senses
The senses put us in contact with the material world and provide knowledge of things we usually accept as true. However, the senses can deceive us. There are numerous illusions and perceptual alterations. Furthermore, hallucinations and other perceptual disorders can lead one to perceive as true ‘realities’ that do not exist in any way. Although, most of the time, our senses report truthfully, Descartes sought an absolutely certain truth as a starting point to construct, by deduction, the rest of knowledge. The potential for sensory deception is the first reason for doubt.
Reason 2: Dream Argument
It is often difficult to distinguish wakefulness from dreaming. We can have dreams so vivid that we believe we are experiencing reality, while our perceptions are merely dream representations. This second reason for doubt leads us not only to question whether things are as we perceive them but also to doubt the very existence of external things. This means we must also doubt the certainty of our own body and the existence of the material world.
Reason 3: Evil Genius Hypothesis
Nothing prevents us from hypothesizing that we might have been created by a powerful and malicious ‘evil genius’ who deceives us. This third reason for doubt extends its reach even to mathematical truths, which might otherwise seem indubitable. The method, requiring radical doubt, thus leads to the provisional rejection of all knowledge: from sensory perceptions and the existence of the external world, to mathematical truths.