Descartes states that every man is equally equipped with “good sense”, which is the faculty of judgement that leads one to wisdom. However, “it is not enough to possess a good mind; the most important thing is to apply it correctly” (p.2). Although each person may be equal in possessing the same forms or nature, everyone uses different methods of reasoning in different ways.
Descartes then provides his own journey in which he found satisfaction only through equipping a philosopher’s eye in the pursuit of truth, and thus fashioned a method. He narrates how he was educated in classical studies in his earliest years and explains that his devotion to the study of the languages, histories, fables of the classical world prevented him from seeing that “everything not in accordance with our own customs is ridiculous and irrational” (p.6). Descartes enjoyed poetry yet thought of it as more of a product of the mind rather than of studies. And, although he was really keen on mathematics, he was unsure of its true use outside mechanical arts. Also, seeing that the path of heaven is open to both the learned and the ignorant, Descartes refused to take the path of theology, which, in the task of studying it, required “extraordinary assistance from heaven, and to be more than merely human” (p.8). As for philosophy, although its history consisted of great minds, the uncertain conclusions of the same mattered proposed by different men dissatisfied Descartes. Lastly, when it came to other disciplines, Descartes saw them built on shaky foundations and done for the sake of honour and profit.
So, as soon as Descartes was able to escape from the control of the teachers, he did; abandoning altogether the study of letters. Fired with the pursuit of knowledge, Descartes spent the rest of his life travelling and observing the different customs of people, showing that he couldn’t trust the certainty of what he had previously learnt. Eventually, having spent some years studying the “book of the world” (p.10), he decided to start looking inward. “In this it seems to me that I have had much more success than if I had never left either my country or my books” (p.10-11).
“At that time I was in Germany, where I had been called by the wars that have not yet come to an end there; as I was returning to the army from the coronation of the emperor, I was halted by the onset of winter in quarters where, having no diverting company and fortunately also no cares or emotional turmoil to trouble me, I spent the whole day shut up in a small room heated by a stove, in which I could converse with my own thoughts at leisure” (p.11). During this time, Descartes reflected on the accomplishments of single individuals compared to that of groups. He realised that buildings with a single architect are more beautiful and better designed than those which different designs have been patched together by various architects; and also how having only one lawgiver gave rise to great nations, such as that of Spartans and the world governed by God. “And so, […], because we were children before we were men, and because for a long time we were governed by our appetites and our teachers […], it is almost impossible that our judgements are as pure or as solid as they might have been if we had full use of our reason from the moment of our birth, and had been guided by that alone” (p.13).
Descartes also observed that people demolished their old houses in order to rebuild them not with the sole purpose of constructing them differently and embellishing the streets but because the insecurities they feel of the building possibly falling down. So, “this example convinced me that it would not be reasonable for an individual to set out or reform a state by changing everything from the foundations up, and overthrowing it in order to rebuild it, or even to set out to reform the body of knowledge or the established order in schools for teaching it; but rather, as far as all the opinions I had hitherto accepted were concerned, I could do no better than to set about ridding myself of them once and for all, with a view of replacing them afterwards either with better ones, or even the same ones, once I had tested them with my reason and ensured that they were set straight” (p.13-14). However, he opposes the idea of toppling public institutions and completely rebuilding them. He merely seeks to discuss his method with the audience, without asking us to imitate his method. In fact, he proposes that the world is made up of two sorts of minds. One of them belongs to those that believe they are more clever than what they actually are and thus lack the patience to govern their thoughts in an orderly way — remaining lost in their lives; and the others are those that have enough sense or modesty in distinguishing the true from the false with the guidance of a teacher. Descartes states that he would have considered himself to belonging to the second group if “I had only had one teacher, or if I had not known about the differences of opinion that have always existed among the most learned” (p.16).
Before abandoning his previous opinions, Descartes constructed four laws that directed his inquiry. “The first was never to accept anything as true that I did not incontrovertibly know to be so […] The second was to divide all the difficulties under examination into as many parts as possible, and as many as were required to solve them in the best way. […] The third was to conduct my thoughts in a given order, beginning with the simplest and the most easily understood objects, and gradually ascending, as it were step by step, to the knowledge of the most complex […] The last was to undertake such complete enumerations and such general surveys that I would be sure to have left nothing out” (p.18-19). But before applying his method, Descartes decided to establish some philosophical foundations to his method.
Descartes, before constructing his method, decided to follow a moral code with four maxims. “[…] in order not to remain indecisive in my actions while my reason was forcing me to be so in my judgements, and to carry on living from then on as happily as I could, I formed a provisional moral code for myself consisting in only three or four maxims” (p.22).
The first “was to obey the laws and customs of my country and to adhere to the religion in which God by His grace had me instructed from my childhood, and to govern myself in everything else according to the most moderate and least extreme opinions, being those commonly received among the wisest of those with whom I should have to live” (p.23). While doing so, Descartes paid attention to what people did instead of what people said “not only because in the present corrupt state of our morals few people are willing to declare everything they believe, but also because some do not even know what they believe […]” (p.23).
Descartes’ second maxim “was to be as firm and resolute in my actions as I could, and to follow no less constantly the most doubtful opinions, once I had opted for them, than I would have if they had been the most certain ones” (p.24).
The third “was to endeavour always to master myself rather than fortune, to try to change my desires rather than change the order of the world, and in general to settle for the belief that there is nothing entirely in our power except our thoughts, and after we have tried, in respect of things external to us, to do our best, everything in which we do not succeed is absolutely impossible as far as we are concerned” (p.25).
Lastly, Descartes reviews the various occupations men have in this life and pick the best one. “Without wishing to pass judgement on the occupation of others, I came to the view that I could do no better than to continue in the one in which I found myself, that is to say, to devote my life to the cultivation of my reason and make such progress as I could in the knowledge of the truth following the method I had prescribed for myself” (p.27).
Having established these maxims, “and seeing that I expected to be better able to complete this task in the company of others than by remaining shut any longer in the stove-heated room in which I had had all these thoughts, I set out on my travels again was over” (p.28). Thus, Descartes spent the next nine years wandering the world, spectating people while reflecting on what might make their thoughts suspect to error. In this manner, he separates himself from the sceptics who doubted for doubting’ s sake as his aim “was to reach certainty and reject shifting ground in the search for rock and clay” (p.29). Finally, Descartes decided to settle and “live as solitary and as retiring a life as I would in the most remote of deserts, while lacking none of the comforts found in the most populous cities” (p.31).
In his pursuit of truth, Descartes decided to “reject as completely false everything in which I could detect the least doubt, in order to see if anything thereafter remained in my belief that was completely indubitable” (p.31-32). Because senses can be deceiving, Descartes decides to abandon sensory knowledge. Then, “and because there are men who make mistakes in reasoning, even about the simplest elements of geometry, and commit logical fallacies, I judged that I was as prone to error as anyone else, and I rejected as false all the reasoning I had hitherto accepted as valid proof” (p.32). Finally, since thoughts can emerge in dreams while we are asleep and do not realise it, Descartes also pretended that “everything that had ever entered my had was no more true than the illusions of my dreams” (p.32). This led Descartes to his famous conclusion. “But immediately afterwards I noted that, while I was trying to think of all things being false in this way, it was necessarily the case that I, who was thinking them, had to be something; and observing this truth: I am thinking therefore I exist, was so secure and certain that it could not be shaken by any of the most extravagant suppositions of the sceptics, I judge that I could accept it without scruple, as the first principle of the philosophy I was seeking” (p.32). In other words, Descartes writes “I thereby concluded that I was a substance whose whole essence or nature resides only in thinking, and which, in order to exist, has no need of place and is not dependent on any material thing. Accordingly this ‘I’, that is to say, the Soul by which I am what I am, is entirely distinct from the body and is even easier to know than the body; and would not stop being everything it is, even if the body were not to exist” (p.33). Thus, the mind-body duality emerged.
In the next step, Descartes, seeing that his being was not perfect, “decided to look for the source from which I had learned to think of something more perfect than I was myself” (p.33). When it came to things such as the heavens, the earth, light, heat, and others, Descartes thought that these things were delusions of the mind. “But this could not be true of the idea of a being more perfect than mine” (p.34). He came to conclude that the idea of a perfect being couldn’t have simply been the product of an imperfect mind but could have only been put into it by the perfect mind, which Descartes claimed to be that of God. This is also known as the ontological proof of the existence of God. Descartes also writes about how the existence of God is akin to the fact that the three angles of triangles add up to 180 degrees. For the fact to be true, a triangle not ought exist in real life, but by reason we reach to this truth. In addition, when it comes to whether all our thoughts, such as thinking that God exists, is merely an illusion—as in a dream—, Descartes states that it is precisely via God’s existence that we can be assured that our thoughts are indeed true, because real things that come from a perfect and infinite being cannot be false and it is God that guides our reason, although we may have falsities in our reasoning due to us being imperfect beings.
In this part, Descartes gives some information about the results that he reached in his investigation of the physical world—which he couldn’t publish at the time due to Galileo being condemned by his heliocentric theory and which he too was sympathetic of.
Descartes is concerned with the nature of light and many aspects of it, such as the sun and the moon, reflection of light through heavenly bodies, human beings as perceiving light etc. While doing so, Descartes does not speak of this world but of an imaginary world — as he says “in order to remove these things from the spotlight and to be able to say more freely what I thought about them without being obliged either to confirm or refute the opinions of learned men, I decided to leave this earth wholly for them to discuss, and to speak only of what would happen in a new world, if God were now to create enough matter to compose it somewhere in imaginary space […]” (p.42) — thus avoiding any theological disputes.
Descartes then moves from the description of inanimate bodies and plants to that of animals, and in particular that of men — touching upon how God formed the body of man with marvellous internal configurations which perform many unconscious functions. Descartes especially spends a great amount of writing in describing the circulation of blood through veins and arteries and how this movement of blood explains many aspects of the body, such as the movement of the muscles, breathing, and thirst.
Then, Descartes explains the major difference between animals and humans — although both possess many similar organs with same bodily functions, which he describes as human’s ability to speak consciously. “For it is a very remarkable fact that there are no men so dull-witted and stupid, not even madmen, that they are incapable of stringing together different words, and composing them into utterances, through which they let their thoughts be known; and conversely, there is no other animal, no matter how perfect and well endowed by birth it may be, that can do anything similar. […] This shows not only that animals have less reason than man, but that they have non at all” (p.57-58). Therefore, Descartes argues for a rational soul that distinguishes us from animals. He ends by saying “when we know how different flies and ants are, we can understand much better the arguments which prove that our soul is of a nature entirely independent of the body, and that, as a consequence, it is not subject to death as the body is. And given that we cannot see any other causes which may destroy the soul, we are naturally led to conclude that it is immortal” (p.59-60).
In this last part of the book, Descartes writes about how it has been three years since he has completed his treatise but decided not to publish it for various reasons — one being afraid of what has happened to Galileo. However, he believes that the improvements that he has made in his method could lead to significant progress in engineering and medicine, which Descartes paid much importance to. Thus, he hoped to make his findings public so that “combining the lives and labours of many, we might together make much greater progress than any one man could make on his own” (p.63). In his method, by finding the first causes of everything that exists in the word, without considering to this end anything other than God alone, Descartes found it easy to explain most straightforward observations. However, when it came to more particular things, he realised the need for contributions of others.
Nevertheless, Descartes decided not to publish his principles of physics during his lifetime “to avoid being given occasion to waste the time I intend to use in acquiring knowledge, either on the opposition or the controversy to which they might subject” (p.66); thus, not being distracted by the potentially hostile reactions which others would give rise to. Although some may say that such opposition may be useful in pointing errors that Descartes may have committed, Descartes responds by saying that “I have almost never come across a critic of my opinions who did not seem either less exacting or less fair than myself. Nor have I ever found any previously unknown truth my means of the disputations that are practiced in the schools” (p.69). In addition to this, Descartes also thought that his work still required some improvement by him for it to be available for others’ contributions. He also fears that people would simply misinterpret his writings as they may prefer appearing knowledgeable rather than acknowledging their ignorance in the pursuit of truth.
For the aforementioned reasons, Descartes refused to publish his the principles of his physics three years ago. But, two reasons have led him to publish his work. First reason is due to the possibility that people may claim that Descartes’ discoveries were false and that Descartes abstained from publishing for this reason. “The other reason that has made me write is that of seeing every day the project that I have, to acquire knowledge, suffering more and more delay; because of the vast number of experiments and observations I need to make, and which it is impossible for me to undertake without the help of others” (p.75). Descartes also explains that he chose to “write in French, which is the language of my country, rather than Latin, which is that of my teachers, it is because I hope that those who use only their unalloyed natural reason will be better judges of my opinions that those who swear only by the books of the ancients” (p.77). Descartes finally states his commitment to devote his life to scientific study and ends the book by the following words “I am making a declaration that I know will not make me worth of esteem in the world, but then I have no desire to gain it. And I shall always consider myself more obliged to those through whose favour I may freely enjoy my time without hindrance, than to those who might offer me the offices in the world which are held in the highest esteem” (p.78).