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Understanding Rene Descartes

Descartes book cover.jpg

This philosophy study guide for Descartes' Meditations on First Philosophy is the seventh  book in the Smart Student's Guides to Philosophical Classics series.


Like the other books in the series, it is much more than an outline or a set of notes and flash cards. It is a book for “smart students” who are serious about understanding and thinking critically about one of the most consequential books ever written in the history of philosophy.


Part I of the book has the complete text of John Veitch's translation of the original Meditations, presented in a way that makes it much easier for a beginning philosophy student to understand and think critically about Descartes’ classic work. Each of the six meditations is divided into smaller sections with sub-titles, followed by Professor Houlgate’s commentary and critiques. Questions for thought and discussion are at the end of each chapter. These questions are intended to help students prepare for examinations and give them ideas and topics for term papers.


Part II takes the student deeper into Descartes’ meditations. It includes two chapters on method, analyses of Descartes’ arguments and comparisons to and criticisms of other philosophers on important philosophical problems and theories. These are presented in a way that invite students to do their own thinking about the meditations, engage with their professor in classroom discussion, and organize and write a successful term paper.

Here is a sample of what you will find in the book::

 Descartes' Proof for the Existence of God

In chapter V of Meditations, Descartes states what is now called The Ontological Argument for the Existence of God.  The argument is called ontological because it derives the existence of God not from experience or matters of fact but from the concept of God.

I should mention that The Ontological Argument did not begin with Descartes. The first version was written by St. Anselm in the 11th century BCE and later repeated by Duns Scotus in the 13th century BCE..  In Descartes’ time, the argument was accepted as valid by Leibniz. But the argument was not received well by some contemporaries of Descartes

Here is a breakdown of the ontological argument in Descartes’ words:

 1. The clear and distinct idea of God in my consciousness is the idea of a being whose nature is supreme perfection.

2. I know with clearness and distinctness that an actual and eternal existence pertains to the nature of a supremely perfect being.

3. Therefore, God actually and eternally exists.


The popular version of the argument is easier to understand:

1. God is an all-perfect being.

2. Existence is a perfection.

3. Therefore, God exists.

            The argument is valid. It begins with a definition of God as “an all-perfect being.”  Premise #2 asserts that the concept “all-perfect” logically implies existence as one of the many perfections possessed by God.  From these two premises,  Descartes can validly conclude that God exists. 


 Rebuttals of the Ontological Argument

Valid arguments are not always sound.  They might contain false premises..  This is exactly what was contended by Immanuel Kant and later by David Hume.


Kant: existence is not a property

Kant’s rebuttal of the Ontological Argument is that existence is not an attribute or property like omniscience or omnipotence. If existence is not a property, then we cannot prove the existence of someone or something by analyzing the concept of that one or thing.  For example, I cannot logically derive the existence of 100 dollars from the concept One Hundred. One hundred real (existing) dollars is the same amount as in the concept. Adding existence to the concept of one hundred dollars does not change the amount in the way that adding one dollar changes the amount and (therefore) changes the concept itself (to One Hundred and One).

By analogy, I cannot logically derive the existence of human beings from the concept of Human. An analysis of this concept will not be sufficient to prove that human beings exist. If 100 dollars and humans exist at all, this can only be confirmed by observation and experience, not by concept analysis.

If existence is not an attribute or property of an object, event, or person, then the idea (concept) of supreme perfection cannot imply that a supremely perfect being exists, any more than being “supremely imperfect” implies that a supremely imperfect being does not exist. Non-existence, like existence, is not a property.


David Hume: existence cannot be demonstrated

David Hume has a slightly different rebuttal.  In his Dialogues Concerning Natural Religion, Hume writes that “there is an evident absurdity in pretending to demonstrate a matter of fact, or to prove it by any arguments a priori.” (55). Statements about what does or does not exist are statements about matters of fact not statements about logical relationships between ideas (concepts).

As matters of fact, statements about the existence of God are no different than statements about the existence of the gods of ancient Greece, for example, the existence of the god Zeus.  Such statements cannot be “demonstrated,” as was attempted in the ontological argument presented by Descartes.   They can only be proved or disproved by observation and experience. 

Hume explains in the same quote that to demonstrate that a proposition is true is to prove it by an argument a priori. I can demonstrate (prove) that triangles have three sides because the sentence “Triangles have three sides” relates one concept (triangularity) to another concept (three-sided shape).  The relation is one of necessity. To deny that a triangle has three sides is to state a contradiction.  To deny that something or someone exists (dragons, fairies or gods) might be false, but it does not state a contradiction. 

[Get your copy now.  Click on the book cover image above.]

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