Rationalism and Knowledge in Descartes

1.0 Introduction
Over the years, the nature of reality, knowing, thinking and believing has constituted puzzling issues which epistemology attempts to grapple with. Issues cutting across what can we know, what is the nature and scope of human knowledge, what can be known with certainty, how do we acquire knowledge, how can we know what is when we come across it, what can be left to faith or opinion to decide, as well as the proper source of knowledge preoccupied the philosophical and at the same time, the epistemological thought of philosophers. In this connection, different schools of thought have come to limelight notably among them are scepticism, rationalism, and empiricism.
For instance, scepticism poses a problem by arguing that knowledge is impossible, that we cannot know anything for sure. To resolve this issue, rationalism puts forward that the process of reasoning is the surest path to knowledge, whereas empiricism says that knowledge is acquired through sense experience. But, “is knowledge actually got through sense experience?” or “is it acquired through the process of reasoning?” or perhaps, is it impossible for us to know? These questions arise owing to the fact that our claims to knowledge are in need of justification for they are challenged by scepticism; doubts about our knowledge claims and doubts about the evidences that support our knowledge claims.
It is in recognition of this that Rene Descartes entitled his magnus opus the Discourse on Method and Meditations. And it is also the reason why he insisted that reason is the ultimate court of appeal whereby our knowledge claims can come to rest and, in fact, be justified. In the light of the foregoing, this essay shall bring to center-stage rationalism and the justification of knowledge in Rene Descartes. To do this, this essay shall pay attention to the basic tenets of rationalism, Descartes’ viewpoint on rationalism and the justification of knowledge, and rationalism beyond Descartes. This will then be followed by the evaluation and concluding reflection.
2.0 The Basic Tenets of Rationalism
It is quite pertinent and absolutely imperative to note that “rationalism is a philosophical school of thought which holds that knowledge is reached through logico-mathematical reasoning.” As a doctrine of the source of knowledge, rationalism is the view that reason is the ultimate source of knowledge; it looks to the world of mathematics from which it draws its model. For the rationalists, the mathematical model being the basis of human knowledge will ward off the challenges of scepticism. They further argue that we will understand a significant body of knowledge about the world and the way it operates through the application of reason. Hence, reason alone, the rationalists conclude, is capable of leading us to certain knowledge. To substantiate this view, they posit that our human knowledge will be certain, logical and endure for all time like mathematical knowledge. Upon their view, “the evidence of the senses should agree with the truths of reason but they are not required to acquire these truths.”
Along these lines, rationalism according to Uduma Oji Uduma “refers to any view appealing to reason as a source of knowledge or justification.” He goes further to distinguish between three kinds of rationalism: ethical rationalism, religious rationalism and epistemological rationalism.
Ethical rationalism holds that ethical principles are not grounded on or derived from emotion, empathy, or some other non-rational foundation. In this case, “reason rather than feeling, custom or emotion is the ultimate court of appeal in judging actions either as good or bad, right or wrong.” Religious rationalism says that all of man’s knowledge comes through the use of his natural faculties, without the aid of supernatural revelation. Epistemological rationalism finally states that man’s knowledge is gained through a priori or rational insight as distinct from sense experience. In all these, it is only reason, the rationalists will argue, that can give us true and absolute knowledge.
3.0 Rationalism and the Justification of Knowledge in Rene Descartes
Rene Descartes was a scientist, a mathematician and a philosopher but his school of thought is rationalism. He is usually called the “father of modern philosophy” owing to the fact that he chose the deductive method because of the attraction that mathematical method held for him. Also, he is the first man of high philosophic capacity whose outlook was profoundly affected by the new physics and astronomy. His mathematical method, for him, is the only reliable path to attaining clear, certain and distinct indubitable truth. For this reason, he applied this mathematical method and his methodic doubt in arriving at an indubitable truth.
Interestingly, Descartes does not accept foundations laid by predecessors, but endeavors to construct a complete philosophical edifice upon which epistemological claims can come to rest. This made him wondered if there were no universal methods of human and scientific reasoning that would open up a new era of scientific truth unshakable by skepticism. Given the impression that the mathematical method is the only reliable path to attaining clear, certain and distinct indubitable truth, Descartes thus felt that “the only uncertainty and confusion we found in philosophy were due to the fact that the past philosophy was founded on doubtful and shaky grounds.” He therefore went further to give philosophy a new beginning, to reconstruct philosophy on a new and firm foundation with the mathematical method as its base. With this, Descartes believed that philosophical confusions, uncertainties and disputes of the past can be set aside. Germane to his mathematical method is the method of systematic or methodic doubt. By means of this method, he swore that whatever he could bring to himself to doubt, he would doubt until he saw no reason for doubting it. He recounts that the philosophical ingenuity in the application of this method is the supposition of imagining a deceitful demon who presented unreal things to his senses in a perpetual phantasmagoria.
The principal motive for the application of the mathematical method and methodic doubt in Cartesian philosophy is to bring into philosophy through an indisputable intellectual speculation the clarity and certainty of ideas and remove once and for all the uncertainties, doubts and disputes in philosophy. For this reason, he writes:
As regards all opinions which up to this point I have embraced, I thought I would not be better than endeavour once and for all sweep them away so that they might later on be replaced either by others which were better or by the same when I had them conform to a rational scheme.

Against this background, Descartes built up a very strong axiom, the cogito which is an indisputable explanatory paradigm by which he arrived at the confirmation of his own existence after series of doubt, not only of his existence but of his body, God and the world at large. Moreover, and consistent with Descartes, the existence of God constituted an adequate causal explanation not only for the reality of his mind but for his body and the external world as well as the physical corporal therein. Certainly, he succeeded, through deduction and the methodic doubt, to prove and confirm his own existence as a thinking thing. He is convinced that the certitude of the cogito ergo sum only affirms that if I doubt, I think therefore I exist. Interestingly, the realization of Descartes’ cogito ergo sum was so certain that the most extravagant suppositions of the skeptics were incapable of upsetting it. This became the underlying foundation and absolute principle upon which he rested his epistemology.
Considering this firm foundation of his, Descartes sets to work to rebuild the structure of knowledge by constructing a system which he bequeathed to modern thought. This system had the background assumption that the order of nature is fixed and stable, and that the human mind acquired mastery of it by operation in accordance with principles of understanding that are equally fixed and universal. To add to this, he posits that
There is a certain disposition of the mind, a certain anxiety expressed in the belief that in our understanding of reality and our interaction with it, only two options are open to us; either we are equipped with some permanent, historical framework to which we can ultimately appeal or we are ineluctably led to relativism, historicism, skepticism and irrationalism. And so, we are always faced with a choice between a certain binding set of ideals and epistemological chaos.

Generally, it was believed that to resolve this anxiety, we required a fixed framework of universal and foundational principles. Realizing this, Descartes embarked on a search for what he called an “Archimedean point” in his Meditations. To this effect, he says:
It is now some years since I detected how many were the false beliefs that I had from my earliest youth admitted as true, and doubtful was everything I had constructed on this basis: and I was convinced that I must once, and for all, seriously undertake to rid myself of all the opinions which I had formerly accepted, and commence to build a new from the foundation, if I want to establish any firm and permanent structure.

In an attempt to establish the project of a securely grounded thought system, he writes in conformity with the vision of Archimedes thus:
Archimedes, in order that he might draw the terrestrial globe out of its place, demanded that one point be fixed and immovable. In the same way, I shall have the right to conceive high hopes if I am happy enough to discover one thing only which is certain and immutable.

From this point of view, he opines that the principles that guide our understanding of the world consist in the correspondence between “ideas” which the human mind found “distinct” and “clear” and aspects of the world. It is in this correspondence that we establish the foundations of knowledge as well as the standard of rationality. Accordingly, at the very base of knowledge is, according to Descartes, the neutral activity of reason whereby knowledge is generated in the individual’s mind acting on distinct and clear ideas.
In his bid to bring into philosophy through an irrefutable intellectual speculation the clarity and certainty of ideas and delete all the uncertainties, doubts and disputes in philosophy, he postulates that the senses are not reliable in giving clear and distinct knowledge. As such, he counsels that “he who seeks for truth must not hope to find it in sense perception, he must ‘detach his mind’ from the sense-nor again in blundering imagination, but in pure intellectual apprehension of infallible truth resistant to doubt.”
He avers that sense experience is nothing but illusions or dreams. He further explains that knowledge of external things must be by the mind, not by the senses. This leads to a consideration of different kinds of ideas. The commonest of errors, Descartes says, is to think that our ideas are like outside things. These ideas for him seem to be of three kinds: (1) those that are innate, (2) those that are foreign and come from without and (3) those that are invented by us. Consequently, he states that the second kinds of ideas are like outside objects which come through sensation and which suppose that a foreign thing imprints on us and so, he concludes that the reasons for supposing that ideas of the senses come from without are therefore inconclusive because such ideas are not seen by a natural light.
Equally, Descartes rejects the Aristotelian logic and affirms that our minds naturally possess two powers which are intuition and deduction. He further argues that “it is through these two mental powers that we are able to arrive at knowledge of things without fear of illusion.” He thus placed the whole edifice of knowledge upon the foundation of intuition and deduction which for him “are the most certain routes to knowledge.” In his opinion, “our senses and our imperfect imaginations leave us confused.” To this end, he asserts that “intuition provides the conception which an unclouded and attentive mind gives us so readily and distinctly that are wholly freed from doubt about that which are understood.” This intuition as a matter of fact does not gives us only clear notions but also some truths about reality, truths that are basic, simple and irreducible. On the other hand, deduction deals with arriving at certainty through inferences from facts. He further explains that through these mental powers, we are able to entirely without fear of illusion arrive at the knowledge of things. It is on these grounds that Descartes rejected sense experience as a deceptive source of knowledge.
On the whole, Descartes left to his successors a new mathematical inspired method in which an emphasis was placed on clarity and distinctness of ideas which are deduced from self-evident first principles. His method of doubt shows that the subjective things are most certain. In all, Descartes justifies his cognitive merit of being a founding father of modern philosophy by opening a new stage in philosophy through a rational principle. This is made manifest in his postulation of the human person as a composite of two different substances namely; mind and body which interact, which, in turn, gave rise to the debates of other philosophical schools of thought.
4.0 Rationalism and the Justification of Knowledge beyond Descartes
Precisely because of truths which belong to the category of empirical knowledge and the notion it poses for the Cartesian notion of clear and distinct ideas, few philosophers will today agree that we can acquire with precision, our knowledge claims only through reason. Particularly, David Hume mounted a massive criticism against rationalism. He contends that reason is limited in giving us knowledge about the physical world. As indicated by him, reason provides only necessary truths, but knowledge about the world involves contingent truths. In his deconstruction of the theory of causation, he dealt a fatal blow to the rationalist enterprise. He argued that we really have no experience of cause and effect but only use the phrase to link two patterns of experiences that frequently occur together. He considers causation as “the feeling of anticipation that rises in our minds when we come to expect one event to follow another, because it has done [so] in the past.” He further argues that no amount of reason will be able to definitely tell us what an effect will follow from a specific cause in advance.
Arguing from an empiricist point of view, he declares that it is only from experience that we come to know how the world works from where we now generalize and propound theories and laws of science. Experience, says Hume, gives us the feelings that one event follows from another. To broaden this view, he, in his introduction of the Treatise on Human Nature, writes, “to me it seems evident that the essence of the mind being equally unknown to us with that of external bodies, it must be equally impossible to form any notion of its powers and qualities otherwise than from careful experiments. It is certain we cannot go beyond human experience.” And so, Hume proposes to say no more on the use of reason in attaining knowledge about the external world.
Other rationalists like Benedict Spinoza and WiIheim Leibniz attempted to save rationalism from the clutches of Hume’s attack on the limitations of reason with regard to knowledge of the physical world. And so, they both argue that empirical truths are necessary truths and as such can be established by reason alone. We shall now consider their respective views on rationalism.
4.1 Benedict Spinoza
Spinoza is regarded as the greatest of Jewish philosophers. He was born into a family of Portuguese Jews and he is credited for his pantheism. For him, “it is reason that settles the conflict between dogma and reality.” He went further to distinguish between three levels of knowledge and describes how we can move from the lowest to the highest. He argues that we can move from (i) imagination, to (ii) reason and finally to (iii) intuition.
His explanations for these levels are as follows; at the level of imagination, our ideas are derived from sense perception or experience and these ideas are very concrete and specific and since our minds are passive, our ideas at this point become vague and inadequate for we know things only as the affect our senses. For Spinoza, this knowledge cannot be a complete knowledge of the real nature of anything since it isolates things from the totality of which they are only parts. He points to the fact that this form of knowledge is not a true and indubitable knowledge. The second form of knowledge goes beyond imagination to reason which he conceives as being limited to the level of scientific knowledge and as such, “everyone can participate in this kind of knowledge because it is made possible by a sharing in the attributes of substance, in God’s thought and extension.” At this level of knowledge, a person’s mind can rise above immediate and particular things and deal with abstract ideas which is logically related and generally deduced from logical deductions. In this regard, Spinoza is of the opinion that “truth validates itself.” So, knowledge here is adequate and true.
The third level of knowledge is the intuitive knowledge which according to Spinoza is the highest degree of knowledge. This knowledge “proceeds from an adequate idea of the infinite attributes of God and it equally represent the knowledge of the essence of things.” At this level, Spinoza deviates from Descartes and argues that there is only one clear and distinct idea from which all knowledge can be derived. As a result, he gave primacy to God as the only absolute substance which is the source of our ideas. He continues that “God is precisely the only substance that exists and that everything is a modification of this substance.”
Though Spinoza and Descartes confute the idea of sense experience as the source of knowledge and accepted the effectiveness of reason as the only source of knowledge, and God as the only living substance. They still differ in principle about the primary source of reason; Descartes on the one hand holds that the mind is the basic source of ideas, Spinoza on the other hand proposes God as the source of our ideas. In view of this, Spinoza speaks of “God as being the cause of all and to this effect, he calls him natura naturans. Also, he calls God’s manifestation in finite modalities both of ideas and bodies natura naturata.”
4.2 Gottfried Wilheim Leibniz
Leibniz proved unmistakable signs of a brilliant mind as a mathematician and the discoverer of the infinitesimal calculus after Newton’s discovery at various occasions affirming that he was a Cartesian. He approaches rationalism in such a way that it proceeds deductively from clear and distinct evidence, and his conception of truth thus puts him in the Cartesian tradition as a continental rationalist. In his epistemological notion on truth, he identified two forms of truth which were analyzed on the basis in which the predicate is contained in the subject.
The first form of this truth is the truth of reason which stems from logic and the fact that its contrary amounts to a contradiction. In other words, this truth deals with purely reason in that “to test the truth of reason, we have to appeal to the law of contradiction,” as a consequence, this form of truth is said to be “an absolute necessary truth” which expresses an absolute identity of subject and predicate, for instance, A is A and A is not A. By this, “it will be contradictory to say that a thing is both itself and its opposite at the same time.” For example, we cannot say that a bachelor is both an unmarried man and a married man at the same time. “Such truths for Leibniz are eternal, essential, metaphysical or geometrical.” The second form of truth is the truth of facts which comes a result of experience. This form of truth is confirmed with the principle of sufficient reason which states that any event can be explained by referring to a prior cause. Also “truth of fact entails the examination of the supposed state of affairs to confirm whether it corresponds with reality.” In this form of truth, its contrary is possible and such truths are contingent or existential based on the fact that it depends upon circumstantial evidence.
More so, in his rationalist epistemology, Leibniz affirms that there is the influence of God. As a result, he points out that God is the source of all reasons, he disputed that “human reason cannot see how the predicate is contained in the subject, nevertheless, God’s knowledge can because it is the very essence of things and so it is absolute and necessary.” The epistemological import of this is that “all empirical truths about the world could be worked out a priori, just by thinking about them.”
Moreover, while Descartes talks about mind and body, Leibniz talks about God, mind and matter as distinct substance. He puts forward that things are complex and are made up of unextended, irreducible, simple substances called monads which are windowless and incorporeal substance whose behaviour are already predetermined. Consequently, monads are unique and dynamic, shapeless, sizeless, individual substance mirroring the whole of the universe in relation to the past, present and future and this as a matter of fact show “the recognition of the significance of reason as the ultimate source of knowledge.” In a nutshell, Leibniz’s conception of truth can thus be subsumed as; truths of reason are known a priori while truths of fact are known a posteriori.
5.0 Evaluation and Concluding Reflection
This essay has attempted an exposition of rationalism and the justification of knowledge using Descartes as a guide. From the study, we have seen that true, certain and indubitable knowledge, according to the rationalists, comes from reason or the ratiocinative process and this as a matter of fact is evident in their unanimous postulation of reason which has to do with the intuitive and deductive method of attaining this indubitable knowledge. Explicitly, Descartes through his cogito arrives at truths which are self-justifying, but he still fell into the criticism of Hume, for as according to Hume, reason is limited in attaining knowledge of the physical world.
However, both Spinoza and Leibniz claim that truths about the world are necessary rather than contingent. In this way, they succeed in escaping Hume’s criticism, yet it does not make their theories criticism proof. They placed necessity on every event in the world by virtue of the existence of a necessary God whom they were unsuccessful to satisfactorily prove His existence. Along these lines, it follows, therefore, that either the Cartesian version of rationalism or the versions of rationalism of Spinoza and Leibniz falls short of establishing that through reason alone, we can arrive at substantial truths about the world or the way things are in the world.
By and large, it is worthy to note that rationalism generally posits that there are rational truths that are eternal and necessary—that we can arrive at these truths through reason and that these truths are self-evident. It is, however, unsuccessful in accounting for knowledge of contingent truths like empirical knowledge and knowledge of the natural sciences, as seen in the attacks of Hume on rationalism. For sure, Man being a rational animal is characterized by the rational faculty or ratiocination as his essence which implies that he comes to know of certain things through reasoning. Yet, we cannot base our conclusion on the rationalists’ position of reason as the ultimate evidence for justifying the primary and sufficient source of knowledge thus making the issue unresolved.
Be that as it may, it could, howbeit, be concluded that epistemology can only be done within the limits of what our faculties can offer. Otherwise, we would fall to what is called the “euthanasia of knowledge.” We cannot acquire knowledge with pure reason alone, it requires both the use of reason and experience.















Bibliography
Ali, S. Ade. “Rationalism and Empiricism as Theories of Knowledge” In Issues and Problems in
Philosophy, edited by Kolawole A. Olu-Owolabi. Ibadan: Grovacs. Network, 2000.

Bernstein, Richard J., Beyond Objectivism and Objectivism; Science, Hermeneutics and Praxis.
Philadelpia: University of Pennysylvania Press, 1988.

Cardinal, D., Hayward, J., & Jones, G., Epistemology: The Theory of Knowledge. London: John
Murray Publishers Ltd., 2004.

Descartes, Rene. Discourse on Method and Meditations. Middlesex: Penguin Books, 1968.

Dunphy, William. History of Western Philosophy. New York: Collier Books, 1976.

Haldane, Elizabeth S. and Ross, G.R.T (eds), Philosophical Works of Descartes. Cambridge:
Cambridge University Press, 1969.

Hume, David. Enquiry Concerning Human Understanding, edited by Tom L. Beauchamp.
Oxford: Oxford University Press.

-------- A Treatise of Human Nature Bk. 1 D.G.C Macnabb, ed. Britain: William Collins
Sons & Co. Ltd., 1962.

Jimoh, Anselm K., Certitude and Doubt A study Guide in Epistemology. Ibadan: Ebony Books &
Kreations, 2013.

Omoregbe, Joseph. A simplified History of Western Philosophy. Lagos: Joja Educational
Research and Publishers Limited, 1991.

Russell, Bertrand. The Problems of Philosophy. New York: Oxford University Press, 1983.

-------- History of Western Philosophy. London: Routledge, 1996.

Stumpf, Samuel Enoch. Philosophy History and Problems. New York: McGraw-Hill, Inc., 1994.

Toulmin, Stephen. Human Understanding, vol. 1. Princeton: Princeton University Press, 1972.

Uduigwomen, A.F., and Ozumba, G.O., A Concise Introduction to Philosophy and Logic.
Calabar: Centaur Publishers, 1995.

Uduma, Uduma Oji. The Fundamentals of Philosophy. Abakaliki: WillyRose and Appleseed
publishing Coy, 2000.