Rationalism is a philosophical system based on methods of inquiry that are grounded in reason, primarily that of mathematical deductive reasoning. Discounting sensory experience as the source of knowledge, extreme rationalists believe that all complex systems of information, such as the truths of the physical sciences and history can be derived simply by thinking about the subjects as consequences of axiomatic principles and their logical corollaries.

Rene Descartes is one of the best known proponents of rationalism. He sought to outline a process of philosophical thought that was independent of the old scholastic and theological traditions of his time. Believing that all sound judgments must proceed from a mathematical basis, he created what is known as The Cartesian Method. Its four basic laws are as follows:

The Cartesian Method

  • Do not accept any propositions as true that are not clear and distinct.
  • Break a problem down into its constituent parts and analyze it as such.
  • Structure thoughts from simple to complex as the order of study.
  • Enumerations must be full and complete with nothing omitted.

This systematic approach is the way that mathematics is structured. Descartes applied it to philosophy with the intention that it might make metaphysical study more clear. Using this method as well as the famous Cartesian statement: "Cogito ergo sum" (I think; therefore I exist), he formed the basis for his metaphysics. He thought that doubt was simply a different form of thought, so "doubting" that one did exist was not a serious threat to validity of that principle. It was the intuitively known axiom that formed the basis for the rest of Descartes' philosophy of Rationalism.

Descartes' next work was with the concept of God, a perfect being in his belief that he sought to prove the existence of. He constructed his proof in the following manner, following his own Rationalist method in order to do so:

The Cartesian Proof of God:

    • I am subject to doubt; therefore I am imperfect; hence I am not the cause of my existence.

    • I have the "idea" of "the perfect." This ideas must come from a perfect Being.

    • The analysis of the idea of "the perfect" includes the existence of the perfect being.1

In terms of ideas, Descartes holds that some ideas come from God; these ideas are innate. Others are derived from sensory experience, and still others are fictitious, that is; they are created by the imagination. He thinks that the only ideas which are certainly valid are those which are innate. All others are subject to fallacy. Also central to Descartes' argument was his notion of the dualism of substances. For a good explanation of his ideas on that subject, see: Cartesian Dualism; it does a good job of explaining it.

Cartesian thought has remained central to philosophy for 300 years; understanding its principles is fundamental to grasping rationalism itself. Descartes left several things out of his line of reasoning; in particular, his analysis of God and his lack of defining the connection between the sensory and rational world. Other proponents of rationalism would attempt to rectify these problems as rationalism was developed further as a philosophic system after Descartes.

Another famous rationalist, Baruch Spinoza, expanded upon the basic principles of rationalism. His philosophy centered on several principles, most of which relied on his notion that God was the only absolute substance; this idea is very similar to Descartes' conception of God. Spinoza argued that God was a substance composed of two attributes: thought and extension. "Substance" in Spinoza's view is something actual, eternal and perceived by the intellect. Any attributes that a substance has define its essence.

Spinoza also defined the term "mode" in his philosophy to be any variations or modifications of that basic substance; essentially they are different forms of a similar thing. He believed that man and all aspects of the natural world were modes of the eternal substance of God. God can only be known through pure thought. This fact is distinctly rationalist; Spinoza thought that the only eternal substance could be known via reason alone, not sensory evidence. In terms of ethics, then, Spinoza believed that all moral behavior could only be defined by the fact that we were variations on the define, so morality had to come through a definition of God's essence.

Gottfried Leibniz was another famous rationalist. Determined to rectify some of the problems that were not settled by Descartes, he explored certain Aristotelian notions and attempted to combine Descartes' work with Aristotle's notion of form. 2 He believed that ideas exist in the intellect innately, but in a virtual sense; it is only when the mind reflects on itself do they actualize. The most basic real substance in Leibniz' view is the monad. Monads are not things of extension, as they are in Spinoza, rather they are things of activity. This activity consists of representation. Apperception is a conscious representation. 3 All activity which is represented in the monads is regulated by God, a being that is also a monad.

Rationalism relies on the idea that reality has a rational structure in that all aspects of it can be grasped through mathematical and logical principles and not simply sensory experience. Ethical and political principles are structures accordingly and are often tied to concepts of God as the absolute for moral conduct. The mind under this doctrine is not "tabula rasa"; it is not a complete blank that is imprinted with evidence provided by the senses. Rather, it is structured by and responds to mathematical methods of reasoning.

The contributions of these philosophers, along with many others, 4 have formulated the majority of the rationalist philosophy. Though tied to such previous philosophical thinkers as Plato and Aristotle and also expanded upon by later philosophers like Immanuel Kant, rationalism remains one of the greatest influences in modern thought since its conception 300 years ago.

1 This proposition was also argued for by St. Anselm.
2 In order to see the connection between Leibniz' and Aristotle's work, it's good to read Aristotle as well. I've noted his delineation of forms, particularly his conclusions about them, to be prominent in Metaphysics, Book VII Chapter 11 1037a 6-34 and Book VIII Chapter 2 1043b 5-25. Also, directly following that section in Book VIII, Book IX of the Metaphysics talks about potentiality vs. actuality and the possibility of innatism; this is particularly important in relation to Leibniz.
3 This is closely related to Immanuel Kant's later exploration of a similar subject. To read an example, see The Critique of Pure Reason, The Transcendental Aesthetic, A27/B43.
4 See Blaise Pascal, Nicolas de Malebranche, Christian von Wolff, etc.

Written for E2 by me courtesy of my old philosophy notes and the following:

Thanks to http://www.radicalacademy.com/adiphilrationalism.htm for the Cartesian proof of God/Cartesian method.

Rationalism, as a "system of belief regulated by reason," might be expected to mean the opposite of irrationality, ignorance, and perverse prejudice. But in ordinary usage, general as well as theological, the use of the word is substantially different. It is generally employed as a term of reproach for those who, without utterly denying or attempting to overthrow the foundations of religion, make such concessions as tend to subvert the faith. They rely, more or less exclusively and blameworthily, on mere human reason instead of simply, frankly, and fully accepting the dicta of the divine word. An atheist would not be spoken of as a rationalist, nor would an irreligious, blaspheming freethinker.

Entry from Everybody's Cyclopedia, 1912.

Ra"tion*al*ism (?), n. [Cf. F. rationalisme.]

1. Theol.

The doctrine or system of those who deduce their religious opinions from reason or the understanding, as distinct from, or opposed to, revelation.

2. Philos.

The system that makes rational power the ultimate test of truth; -- opposed to sensualism, or sensationalism, and empiricism.



© Webster 1913.

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