Best known for the quote from his Meditations de prima philosophia, or Meditations on First Philosophy , "I think therefore I am," philosopher and mathematician Rene Descartes also devoted much of his time to the studies of medicine, anatomy and meteorology. Descartes is also credited with designing a machine to grind hyperbolic lenses, as part of his interest in optics. Rene Descartes was born in in La Haye, France. He began his schooling at a Jesuit college before going to Paris to study mathematics and to Poitiers in to study law.
Uniform Title Discours de la methode. Medium [microform] Physical Description , p. Series Early English books, ; Early English books, ; Subjects Science -- Methodology -- Early works to Notes Translation of: Discours de la methode. Written by Rene Descartes. Available electronically as part of Early English books online. Ann Arbor, Mich. View online Borrow Buy. Set up My libraries How do I set up "My libraries"?
CARM Centre. Book; Microform English Show 0 more libraries None of your libraries hold this item. Descartes has prepared the way for this. The former was already well known, but the sine law for refraction was newly discovered. Huygens was later to complain that Descartes had not referred to Snell, who is now generally credited with the discovery of this law. Descartes carefully shows how the lens of the eyeball, in conformity with the law of refraction, focuses light arriving from the object to form the image on the retina.
The more particular biological facts of sight can be explained by the more general laws of geometrical optics. The sine law of refraction is the general form of a set of laws: the angle of refraction will depend upon the particular transparent substances through which the light passes. The actual angle for any pair of substances will have to be determined by experiment.
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Notice the structure of these inferences. There is a general law to the effect that for any situation of certain generic sort, there are specific laws that have some generic form. This is a law about laws. These two Principles provide a framework within which the scientist searching after truth works as he or she attempts to locate the law of the relevant generic sort that is there, according to theory, to be discovered. There will be a number of specific possibilities, each of the relevant generic sort.
The un-eliminated hypothesis will be the specific law one is aiming to discover. In particular, such experiments will determine the constant of refraction that the sine law asserts to be there for specific pairs of transparent substances.
A Discourse of a Method for the Well Guiding of Reason and the Discovery of Truth in the Sciences
Experiment will confirm the un-eliminated specific hypothesis, and this will in turn confirm the more generic theory that predicted the existence of a law of that relevant form. The direction of the light rays as they pass from one substance to another will be determined not just by the constant of refraction, but also by the curvature of the surface that is the interface boundary. Descartes shows how the shape of a lens contributes to the formation of images. This again is a generic description of the laws applying to many specific situations.
Descartes applies this knowledge to account for the various effects that can be produced on the image on the retina, for example, by squeezing the eyeball to distort the lens of the eye in various ways. Descartes is using the knowledge of patterns not only to explain things newly noticed in observation, but also to apply it in ways useful to the further scientific exploration of the world telescopes and to make ordinary life better corrective lenses. The laws about laws that are the laws of reflection and refraction are themselves laws of physics, laws of matter in motion.
This kinship is not only one of shape but one of the generic form of the laws that describe the motions of these two sorts of entity. He assumes that the particles of light move in straight lines. In the case of reflection he assumes that the light, that is, these light particles, strike an impenetrable surface and bounce off. In the case of the refraction he assumes the particles pass from a medium of one density to and through one with another density.
The deductions Descartes offers are, in particular in the case of refraction, of questionable validity, but that is not to the present point; our interest is in the Cartesian method or methods and not how he actually applies them. Descartes is clearly open to speculation because the model he uses for light is one that lacked empirical confirmation.
He offered little evidence for his model of light. But it has two uses. One is as a heuristic device, to be used to discover laws, such as that of refraction, which can themselves be confirmed in experience. The experimental confirmation of these specific laws will also confirm the laws of the generic theory that has been discovered by means of the heuristic model. He was clear, in his own mind at least, that the model had hardly be given a demonstration in the sense in which one could give in geometry the sort of demonstration given by Euclid. He wrote to Mersenne:. You ask me whether I think what I have written about refraction is a demonstration.
I think it is, at least as far as it is possible, without having proved the principles of physics previously by metaphysics, to give any demonstration in this subject But to demand that I should give geometrical demonstrations of matters which depend on physics is to demand that I should do the impossible.
For, in such matters, one is satisfied that the writers, having presupposed certain things which are not obviously contradictory to experience, have besides argued, consistently and without logical fallacy, even if their assumptions are not exactly true. Many explained that sight occurred by immaterial sensory species, images of the objects being observed, being given off by those objects, and impinging upon the eye. The challenge was more or less that something like this must be so because no purely material explanation, in terms of particles interacting mechanically, could be given for the person becoming aware of the form of the object viewed.
We need not pursue the line of the perceptual process from body into mind. It was based on dissection, mainly of animals, and some experiment, and a good deal of speculation. Overall, it argued the thesis not only that the parts of the body are useful to the survival and good life of the animal or human being, but more strongly that the existence of these parts was to be explained by their utility--they existed in virtue of the fact that they contributed to the Good.
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While connected to the past, the cause of their existence was the form of the Good, their final cause, drawing them from the future into the present. While rejecting the anti-theological positions adopted by these latter Greek and Roman philosophers, Descartes sided with them in opposing teleological explanations. To be sure, anatomy and physiological processes did contribute to the survival and well being of animals and human beings, but their explanation was entirely in terms of mechanistic causes.
That is, the science of human physiology is the same in kind as the science of stones. Descartes was prepared to extend his guess to the whole set of natural processes defining the human being save for rational thought and action under control of the conscious will. The complex mechanisms are assumed to be able to approximate those of a human, but as it is imagined as a machine we will not be tempted to attribute its motions to the various mysterious powers, vegetative and sensitive souls, and so on, as did Aristotle and the Scholastics.
The Description is a more curious work, dealing with the development of the human being from sperm through fetus to grown adult person. It consists mainly of assertions and coarse sketches of the mechanisms supposed to be involved. Still, there were those who were not convinced. The English philosopher, Henry More, was one of these. He argued that the complexity of the human body and activity, indeed the complexity of plants and animals, could not be accounted for in terms of the bouncings and collisions of billiard balls of different sizes.
Needless to say, these plastic forms were non-empirical entities. The idea is with us still, with those who deny the inadequacy of natural selection to explain the origin of complex biological mechanisms. This was especially true of the Cartesian account of the development of the fetus: the passage of information from the sperm to the developing organs begged for the idea of an immaterial Form or final cause pulling the matter together into a whole unlike in any way its genetic antecedents.
More thought this way. He could not envision a more complicated physics, one that included the molecular biology of DNA molecules materially embodying the required information. A physics much more developed than Descartes and More could conceive, certainly much more than the levers and billiard balls and flowing fluids that formed the limits of their vision. But while, in the end, physics went well beyond that limited Cartesian concept of the laws of physics to the laws of quantum mechanics and of molecular biology, these are still the laws of physics and it is still physics which forms the basic patterns of causation in physiology.
He indicates the need for a background generic theory to guide research by providing a principle of determinism and a principle of limited variety. Descartes is well aware of the logical structure of the research process for investigating the natural world, and discovering the laws of that world.
The background theory that is needed is the thesis that the world operates through mechanical processes and mechanisms that obey the laws of physics. Discoveries such as that of Harvey confirm these generic laws that guide the research. But there is more to it than that.
This is where Descartes slips from the idea of science as empirical to the idea of science as a priori, from the idea of science as a method rooted in observation and experiment to the idea of a science whose method is rooted in the demonstrations of pure reason. Descartes argues that the laws in the basic mechanistic framework that he takes to hold for sciences like optics and physiology — these laws about laws that guide empirical research in these sciences — are not themselves empirical but are rather necessary truths that are knowable a priori.
Thus far we have seen that Descartes is well aware of the logical structure of the experimental method in natural science. To that extent he is not a philosopher who asserts that the a priori method applies everywhere.
But he is nonetheless correctly to be counted among the rationalists. In fact he argues that in principle at least all laws could be known a priori. It is just that the world of ordinary things is too complicated in its structure for us, with our finite minds and limited capacity to grasp the a priori structure of the world, to deduce from self-evident premises the laws of the mechanisms underlying ordinary observable things and processes.
But what those specific laws are requires empirical research; they are too complex logically to be knowable a priori by us, with our finite capacities. Descartes argues that all things, including the material world we know by sense, have an inner essence or form, and its presence explains the structure of things as they ordinarily appear. These essences or forms are known not by sense but by reason. Reason is precisely the capacity to grasp these essences which are the reasons for things, the reasons why there are these patterns and regularities in the sensible world rather than others.
He takes for granted that when the form is known that form is literally in the mind of the knower: there is an identity of the knower and the known. To grasp the essence of a thing is to know a priori the structure and behavior of the thing of which it is the essence. Material things are all modes of a single substance, the essence of which is extension. When we grasp the axioms of geometry as necessary truths, we are grasping the logical and ontological structure of the material world. Descartes is like Aristotle in attributing essences to things, but for Aristotle knowledge of the essence is given by syllogisms and by real definitions of species in terms of genus and specific difference.
For Descartes, the structure is given by the truths of geometry. These laws, he suggests, can be deduced from our knowledge of God.
A Discourse of a Method for the Well Guiding of Reason by René Descartes
He creates a world the essence of which is given by the laws of geometry together with the principle that in any change quantity of motion is conserved. This conservation principle is thought to follow from the unchanging nature and stability of God the creator. There is a much more detailed derivation in the Principles of Philosophy. It is far from adequate. Many have thought so.
Discourse on Method Quotes by René Descartes
Descartes had been able to present only a set of non-mathematical principles, but Newton demonstrated that the vortex account, whatever its pretensions to being established a priori, was, given his three laws of motion, inconsistent with the facts of elliptical orbits as established by observation by Kepler. It became an historical curiosity. Be that as it may, it could be concluded that Descartes had merely misapplied his method a priori, not that it was incorrect. Some later thinkers such as William Whewell argued this point.
The method did not disappear in the way the vortex theory disappeared. In one sense, this method is like the method of geometry that Euclid had given to the world in that one began with self-evident truths as axioms and then deduced by equally self-evident steps a set of theorems. The mechanistic framework for carrying on empirical research followed.
However, there is the issue of how the premises are discovered. Euclid never showed how this was to be done. Having reached the theorem, one has constructed a demonstration of that proposition. This synthetic method takes as given the premises from which it starts. But often to find a demonstration one must locate the premises from which the demonstration is to be constructed.
This task of discovery was the point of the analytic method. On this method, one takes the conclusion to be demonstrated not as something accepted as true but merely as an hypothesis. One then works deductively towards the premises which one hopes to find for constructing a demonstration. Having arrived at the appropriate self-evident premises, one reverses the steps to obtain a synthetically organized demonstration of the hypothesis from which the analytic process started.