A brief summary of the Epistemological and Metaphysical systems of the Modern Philosophers
The Continental Rationalists
Although both the Empiricists and the Rationalists shared many common ideas, the Rationalists are so named due to their emphasis on reason as the sole infallible way to obtain knowledge. Some of the philosophers who fit under this banner are Malebranche, Descartes, Leibniz, Spinoza, Wolff, and D’Alembert. However, just because they can all be called rationalists does not mean that they all hold to the exact same views on epistemology and metaphysics. In fact, some of their systems are so different, that there are only a few common threads that hold them together. These threads, however, are foundational to their views, and important enough to be used as a way of distinguishing them from other philosophers. We will look at the main threads that are used to distinguish them from the empirical philosophers, first in epistemology, and secondly in their metaphysics. We will follow this order due to the fact that their metaphysical systems are built upon their epistemological views. Our exposition of Rationalism will be based primarily on Descartes, as the model rationalist.
Following Descartes, all of the rationalists (and, in fact, even the empiricists) claim that the idea is the direct object of the human knower. This may partially be due to the fact that Descartes claimed that philosophers should always seek clear and distinct ideas, which leave no room for doubt. Descartes, based upon this claim, set out to discover the first principles upon which all knowledge could be founded. These first principles were supposed to be knowable a priori by reflection.
In order to be a first principle, the idea must be clear, distinct, and indubitable, and the foundation of all knowledge, though it itself need no foundation, except perhaps that which may be found in God. When such principles had been found, the philosopher could then proceed to deduce all knowledge, based upon these principles.
This is the method that Descartes then put into practice and upon which his entire philosophical system is built. He began with methodological doubt; doubting everything that was neither clear nor distinct. It is, of course, unclear what it means to be clear and distinct. This principle seems to be the only thing that he did not doubt, and as such should be considered the foundation of his entire system. It also became somewhat of a ghost in the machine, which has continued to haunt all philosophical endeavors since Descartes.
Having found that he was able to doubt all of his sensible experience, he arrived at the conclusion that the only thing that he could not doubt was his own existence. However, what he meant by “his own existence” was not his human existence as a mind and body, but the existence of his thinking ego. From this discovery came the most well-known words that Descartes ever wrote, “I think, therefore, I am.”
From this discovery Descartes set out first of all to discover the existence of God, and, secondly, the existence of a mind-exterior reality. As the history of philosophy shows, he was not successful with these endeavors, though his attempt is most informative. Starting from inside one’s intellect, we may be able to know the existence of one’s own intellect, and, perhaps, with enough ingenuity, God’s existence (and Descartes presents some interesting proofs for the existence of God); yet, if the direct object of the knower is the idea, regardless of how clear and distinct it is, the knower can have no access to any mind-exterior reality. According to Descartes our senses are not trustworthy, nor capable of delivering trustworthy information to the knower, so, the knower is trapped in his own mind, with no way out.
Descartes sought to supplant scholastic philosophy, and to start over again. From Descartes on, all of philosophy has been trying to get out of the cogito of Descartes. The basic epistemological claims of Descartes are essentially the same as those of all the other rationalists, though they have, in certain cases tried to find ingenious ways of getting from the cogito to the real world. In summary, then, the epistemology of the Rationalists made the following claims: (1) the direct object of the knower is the idea; (2) All knowledge can be deduced from a priori first principles which are clear, distinct, and indubitable, ideas.
When it comes to metaphysics the rationalists are divided into two main camps. Some, such as Descartes, are technically realists (though, epistemologically they are idealists), because they claim that there is a mind-exterior, mind-independent, reality, and they try to discover a way to know it. Others, realizing the futility of the attempt to know any mind-exterior reality, or, realizing that any “experience” of a mind-exterior reality is dependent on the mind (either the human knower or the divine knower), conclude that even if there is a mind-exterior reality that is independent of the knower, we cannot know it – these are the idealists. Their views are so distinct that it is almost impossible to sum them up in a couple sentences. The basic thread that runs through them all is that, somehow, reality is rational, and mind-dependent. Some of these idealists claim that what we “know” as a “mind-exterior reality” is actually a result of the action of God putting ideas in our mind; others claim that it is just a projection of our own minds. In fact, the extreme monism of Spinoza, by which the entire “world”, all that we “perceive” as existing, including ourselves, is an emanation from God, is a direct consequence of the Cartesian system, in which the main tenet is that rationality is the essential characteristic of being. Of course, not all the rationalists wanted to go to the extreme that Spinoza went; Leibniz tried to save the rationalistic system, but once we begin by claiming that ideas are our only indubitable source of knowledge extreme monism is just around the corner.
For the early rationalists, the existence of God was almost a given. Some of them gave proofs for the existence of God, such as Descartes. However, for many of the idealists, everything that existed could only be explained as emanations from God, thoughts in the mind of God, or direct interventions, on a constant basis, by God. Of course, as some of the phenomenologists after Kant (who have many similarities with the rationalists) were to discover, as long as we remain within the Cartesian claim that ideas are the direct objects of the knower, the existence of God, as the Christians view him, is simply not necessary.
The British Empiricists
We turn, now, to the British Empiricists, who are so named due to their emphasis on experience as the source of all knowledge. Though they shared many principles with the rationalists, they rejected the idea that all of philosophy, and indeed all of man’s knowledge, must be built upon some a priori first principles. Some of the empirical philosophers are Locke, Hume, Bacon, and interestingly enough, Berkeley, who developed a system of spiritualized empiricism. The primary difference between the rationalists and empiricists is their claims about the source of knowledge. We will be using Hume as the model Empiricist.
We will begin with their epistemology. The first thing that we need to notice is that though the empiricists reject the idea that all knowledge is based upon, and deducible from, a priori first principles, they accept, uncritically, two elements of epistemology from Descartes. They accept, first of all, the claim that the direct object of the knower is the idea. However, they claim, and this is why they are empiricists, that the idea is formed in our minds based upon sense impressions, not a priori principles.
Secondly, they accept the claim that Descartes makes about the distinctness of ideas. Therefore, Hume is able to say that our knowledge comes from sense impressions which create in our minds, ideas. In meeting the outside world, man receives simple impressions, which are either from sensation or reflection, and are the sources of our ideas. Simple ideas, which come from simple reflections, can be combined into complex ideas. If the impression is “vivid” enough, then our ideas will be clear & distinct, and easier to remember, and think about.
What the empiricists call the imagination is the faculty of the mind that works with ideas, both simple and complex, and helps us to make sense of our sense impressions. All those ideas, which are found in the imagination, which are distinct and clear, can be traced back to some vivid sense (or reflective) impression, and can be said to be of some existing thing. All knowledge, therefore, comes from either sense impressions or reflection on ideas, but, the direct object of the knower is the idea. Even with the empiricists we still have no direct access to mind-exterior reality, even though all of our knowledge comes from it. The question inevitably arises (Both Russell, and Wittgenstein, later attempted to answer this question, without success. Though, Wittgenstein correctly noted, in the Tractatus Logico-Philosophicus, that in order to have true knowledge we must be able to get past, what he called, the pictures of reality in the mind, to reality itself.), how do we know that what our senses are “telling” our imagination corresponds to what is actually outside our mind? For Hume, the answer, showing Descartes influence on even the strictest of empiricists, has to do with the distinctness of the idea, which is a direct result of the vividness of the impression. We are still trapped, even as extreme empiricists, in the cogito of Descartes, though it has taken on a slightly different flavor.
Having shown how it is that man knows, the empiricist is now ready to talk about the nature of reality. That there is a mind-exterior reality is a given, because all of our knowledge is based upon sense impressions of the outside world. We don’t have direct access to reality, only to our impressions of it, but reality is still there. For the empiricist, because everything that exists is known only through our sense impressions, anything that cannot be sensed, cannot be known. Therefore, whether or not it exists, if we can’t have sense impressions of it, then we cannot talk about it. Upon this basis, all the elements of traditional metaphysics are thrown out the front door. We cannot sense causality; therefore, it is purely a notion that is created by our imagination in order to explain the seeming “connectedness” of events in our sense impressions. We cannot have any sense impressions of God; therefore it is useless to talk about his existence or nature. Due to the fact that causality doesn’t exist outside of our minds we cannot deduce from it the existence of God. In fact, it is pointless to talk about the unity of the world and the self as we have no sense impressions of such unities. All of the notions of traditional metaphysics are creations of the imagination as it reflects upon the ideas that are formed from the sense impressions. As such, they do not correspond, as far as we know, to anything in reality, it is, therefore, useless to talk about them.
Such a pure empiricism is, of necessity, nominalistic, as it must reject, as part and parcel with traditional metaphysics, all universals, the idea of necessity, and even the notion of some underlying substance.
Unable to get out from under the guiding principles of Descartes (distinctness of ideas, and ideas as the direct object of the knower), the empiricist ends up, inevitably, in skepticism.