A&O READING on Descartes Radical Doubt


on Radical Doubt

Tom Drake teaches Western Civilization at Idaho and has a nice summary of Radical Doubt (Drake 258)

Radical Doubt, Analytical Method and Empiricism: Shaping the Modern Mind, and Marching Toward the Scientific/Technological Revolution


In many ways Descartes takes Platonic philosophy and formulizes it along secular lines to produce the foundation of modern philosophy and scientific reasoning. Locke’s empirical approach will round this out, and Newton will apply it to affirm its validity.  Voltaire will bring these concepts together, and to Europe, and use them to revolutionize human relationships.

Descartes Discourse on Method 1637

Cogito Ergo Sum

“The long chains … [math’s ability to simplify and correctly work thru exceptionally difficult problems] … had given me reason to believe that all things which can fall under the knowledge of man succeed each other in the same way [all things can be understood thru mathematical reasoning/principles], and provided that…[the method is correct…we can understand all things this way]”


“…to apply them [agreed upon mathematical principles] to every other subject to which they should prove suitable…everything was so complex I should express them with numbers (simplicity)…I should borrow all the best in geometrical analysis, and in algebra…”

In other words, we should apply mathematical principles to understanding everything. 

Descartes broke his “method” down into four parts: (Kemerling)

1.  Systematic Doubt:  Question everything and all previous authorities.  Accept as true only what is absolutely certain.  This is perhaps his most radical and basic step: the foundation of all scientific thinking. (For the sake of English 258, this is what we’re most interested in.)

2.  Analysis:  Divide every question into manageable parts and name the parts. Assign symbols (as in numbers etc.) to elements, so that they can be better understood and managed (think of using calculus to understand economies, the movement of planets, light…etc etc).  Consider how impossible it would have been to complete the human genome project or invent modern medicines without this approach: there would never have been a periodic table of elements to begin with.

3.   Synthesis or Deduction via the test of Rational Intuition:  Begin with the simplest issues and ascend to the more complex.  Start with things you can prove and work from there; make no large assumptions upon which to base a theory.

4.   Avoidance of Deductive Error:  Review frequently enough to retain the whole argument at once.  Re-test, re-test, re-test to ensure that you don’t have to much confidence to your theory; continually look for empirical means to test it.

In addition to this method, Descartes came up with some underlying assumptions as well: (Warren) 

1. Nature itself has a geometrical-mathematical order or form (the assumption of the new field of physics)— this is a metaphysical view about the nature of existence itself (ontology).

2. All knowledge can be ordered or organized geometrically (i.e. that all our true judgments or beliefs are rationally connected like the parts of a geometrical demonstration).  This is an epistemic view: a philosophy concerning what true knowledge is and how it can be found.

3. Only when our understanding takes on a geometrical-mathematical order or form can it represent correctly the real nature of things—also an epistemological view.

These assumptions profoundly effect Enlightenment philosophers: by understanding the inherently logical/mathematically perfect order of the universe we can understand man’s place in that universe and we can govern ourselves — and each other? — accordingly.


“Radical Skepticism”: Cogito Ergo Sum = I Think, Therefore I Am.

a) Do not assume anything

b) Reject as “truth” that founded only Authority (people have prejudices and make errors, even in math, where we can prove that the errors are human and not objective)

c) Reject as “truth” subjective (un-test-able) perceptions.


So how do these translate into “the cogito”?  If the true skeptic doubts everything, he must doubt the reality of his own existence, and so Descartes does, then attempting to come up with rational “proof” of his own existence.  He famously deduces that if there is someone asking the question “Do I exist” there must be someone doing the asking;  all other explanations are rationally false (someone cannot ask if he exists unless there is someone to do the asking).  In other words, someone is thinking about whether or not he exists, and this proves he exists.  Yeah, I agree: this sounds more like Dude, Where’s My Car? than it does philosophy, but whatever.

Descartes on God:

Deduces that God Exists (408): “I bethought myself to find out from whence I had learned to think of something more perfect than I; and I knew for certain that it must be from some nature which in reality was more perfect….  I could not derive it from myself; so that it remained that it had been put in me by a nature truly more perfect than I…God.”

The logical error in this deduction: Descartes violates his own “radical skepticism” from the previous pages: the concept of “perfection” or “more perfect” is a concept (an idea), and not necessarily a thing that can be observed. We can directly observe people forming false concepts (the world is flat; women are inferior to men etc.), so the idea/concept “perfection” does not prove the existence of perfection itself, only the existence of the idea itself.  So, Descartes’ own method proves the existence of the concept, not the “thing itself”, “God”.

Locke: (1632-1704)

Essay Concerning Human Understanding 1690

Tabula Rasa


421 Not born with knowledge (“No Innate Ideas”); born with a “tabula rasa”: blank slate. This is a direct response to Plato’s theory that man is born with innate understanding of the “Ideals”

422 All knowledge derived from EXPERIENCE: SENSATION OR REFLECTION

Sensation: perception of objective world; what we learn from experiencing reality thru our senses.  Note that this would include what we receive thru language — what others tell us, write etc.

Reflection: “the notice which the mind takes of its own operations” (what we would call “consciousness” or simply “thinking”). Note: this “reflection” includes “passions” (what we would call “emotions”).

“These two … [Sensation and Reflection] … are to me the only originals from whence all our ideas take their beginnings.”

Note mammoth political/social (and psychological, educational etc.) implications:  Intelligence is a product of environment (experience), not birth, social class, lineage etc.  Intelligence is accessible to all.  Thus: “all men are created equal.”

We are also interested in how this theory sets the platform for Locke’s most important political contribution: tolerance.

Newton (1642 – 1727) :

Newton takes Descartes’ philosophy (the Cartesian Method), formalizes and perfects it, and proves it by combining it with Empiricism (observation, Locke etc).

Philosophiæ Naturalis Principia Mathematica (“Mathematical Principles Of Natural Philosophy”) (1687)


         — Invents calculus: the analytical method Descartes’ said we should use to simplify human thinking: (note: calculus is simultaneously created by Leibnitz)

       — Formally applies mathematical knowledge to explaining physical phenomena: focus on purely factual laws describing physical phenomena: applies Descartes’ Method, proves mathematical principles can explain natural phenomena/universe

         — Uses experiment (empiricism) as basis of knowledge. Knowledge not based on hypothesis alone but on observationverified through symbolic logic (inductive basis of science: facts lead toward theories): applies Locke et al’s empiricism.

In so doing he develops what is often called:

         — The first “mind without metaphysics”; or we could say he takes the “meta” out of “metaphysics”: that is to say, Newton is the first to explain the workings of the universe without defaulting to faith or God or “the Gods” etc.

When pushed to explain why the laws of physics are what they are (a metaphysical question), he famously replies “I don’t know.” In other words, he adopts Descartes’ view that we should not call assumptions knowledge: we only “know” those things that we are able to prove and accept as certain; he sticks to self evident truths.


Note how these open the doors to:

1) Harnessing The Scientific Revolution.  These ideas finalize the philosophy and science and paint the way for an explosion in scientific exploration, knowledge and application; essentially, these philosophies unlock Galileo’s genius and make it something anyone can learn and apply to any question concerning the natural universe.

2) Democracy: Thomas Jefferson bases the fundamental constitutional premise that “all men are created equal” upon Locke’s philosophy of “no innate ideas”: regardless of gender, race, class or religion, we are ALL born with a tabula rasa, and therefore knowledge/truth becomes accessible to all who can learn and apply the methodology.  Democracy, like science, is also predicated on skepticism: never fully trusting the word/findings of previous authorities.

3) The Industrial Revolution: Once clearly defined and established through fact, these ideas spark a revolution in applied knowledge: technology.  Descartes, Locke and Newton etc. don’t just make it possible to study the universe but to harness its power and engineer its structure.

It’s safe to say that without these emerging Enlightenment philosophies, we would still have king or queen, we would still have slavery, you would not be able to vote, our legal system would be almost entirely based on torture, we would have no electricity, no motors of any kind running on coal, steam, fossil fuels etc., we wouldn’t have toilets and running water, medicine would still consist almost entirely of leeches and prayer and nearly every person in this class would die by the time he or she reached 30…75% of all children would die before the age of 5….