Ports of Call


Descartes 1

Descartes -- Science and skepticism

First Sightings

Readings for this part of your journey

You are going to read much of Descartes'Meditations. For this first unit you will be reading Meditations I and the beginning of II.

In this section of the course we are going to look at Descartes' efforts in the Meditations on first Philosophy to show that there is knowledge of which we can be certain of the self, God and the external world. Descartes was an important figure in the development of modern science. He had a mechanistic physical theory which was Copernican at its heart. In trying to put knowledge of the external world on a firm foundation, Descartes may be making an effort to show that basic features of his own physics and cosmology can be known to be true with certainty, as can the real distinction between the mind and the body. Thus, one way of approaching the Meditations is through the development of modern science. Among the intellectual developments during this period, the rise of modern science is at the top of the list in importance and influence on making our world what it is, for good or ill. It is thus important in itself, but Descartes also fits into this story in important ways.


The birth of modern science

A Spanish historian writing some fifty years after the voyages of Columbus, remarked of those voyages that nothing had happened of such importance in the history of the world since "the birth of our Savior."
A modern historian of science, reflecting on the development of modern science in the sixteenth and seventeenth centuries, remarked that nothing had happened of such importance in European cultural history since the advent of Christianity. Here we have one of the bases for the analogy between the voyages of discovery by ship and the intellectual voyages of discovery. Rene Descartes was a major figure in the birth of modern science.

In the sixteenth century, European mathematicians reached the point where they surpassed the ancient mathematicians -- Euclid, Archimedes, and Apollonius. The ancients had left a series of unsolved problems. European mathematicians either solved those remaining problems or showed that they could not be solved. There was a movement in progress to treat arithmetic and geometry algebraically which was to lead to the development of the calculus. Similarly, astronomical thinking during the sixteenth century broke with ancient models. Copernicus, mentioned by Montaigne in An Apology for Raymond Sebond published his book suggesting that the earth and other planets moved about the sun in 1543. The Copernican system challenged the Aristotelian and Ptolemaic view of the universe. It replaced the earth centered Ptolemaic view with a sun centered one. That Ptolemaic view also held that all change was confined to the sublunar sphere. Beyond the moon the planets, the sun and stars revolved around the earth in unchanging crystal spheres. This view of the universe had been integrated with Christian theology by Thomas Aquinas in the thirteenth century.

Tycho Brahe
Later in the sixteenth century a Danish astronomer, Tycho Brahe, engaged in the most painstaking observation of the positions of the planets (and in particular Mars) up to that time. He did this without the aid of a telescope. Brahe knew the Copernican system, but did not accept it. He had an account of his own which was neither Ptolemaic nor Copernican. One of the things he observed in the 1680s was the vast explosion of a star -- a supernova. This suggested that the Aristotelian/Ptolemaic view that the realm beyond the moon was unchangeable was false.
Johanes Kepler
Brahe's observations were inherited by his German assistant, Johan Kepler. Kepler, a Copernican, eventually discovered that the orbits of planets around the sun were elliptical rather than circular and developed three laws of planetary motion. Kepler also did work in optics which was to help establish the reliability of the telescope. Given the importance of optics, we should not be too surprised to discover that Descartes, Newton and Berkeley all wrote books about optics. Descartes made both important theoretical and practical contributions to the making of lenses. Light is enormously important in optics, and it is central to Descartes physics. The three kinds of matter in his physical system can be understood as light, the medium through which light is transmitted, and that which reflects and refracts light.

It is not too surprising that the Copernican system met stiff resistance. It had quite unsettling implications. That the earth orbits the sun seems like a trivial piece of factual knowledge to us. At the time, however, it was fairly difficult to determine which of these two theories was the correct one. The fact that the sun seems to rise in the east and set in the west was compatible with both theories. Galileo had not yet made a telescope and pointed it at the heavens.
This would not happen until 1609-10. By discovering features on the moon such as mountains and craters, for example, Galileo reinforced the analogy between the earth and other bodies in the solar system. This was also the import of Galileo's discovery of the moons of Jupiter. Other planets, like the earth, had bodies orbiting around them. So, the earth was like these other bodies. The Crystaline spheres were shattering. Even after Galileo reported these discoveries in the Starry Messanger, however, there were doubts about the reliability of the telescope that had to be resolved.

Galileo also played an important role in the development of physics. Like Raymond Sebond, he viewed nature as a book, but in his view the language of the book was mathematics. The ancient Greek and Roman atomists had distinguished between sensible qualities, such as color, taste, smell and sound, which were dependent on a relationship between atoms and organs of perception for their existence; and other qualities such as occupying space, being in motion or rest, and others, which were qualities existing independently of any perceiver. Galileo adopted this distinction. Galileo also came very close to the most fundamental physical discovery of all, the law of inertia -- that bodies at rest tend to remain at rest and bodies in motion tend to remain in motion. This law, the most crucial discovery in the development of modern physics, ran counter to Aristotelian physical theory. Galileo formulated the law of intertia in terms of circular motion. It remained for Descartes to give the law its modern formulation.

The development of mathematics, astronomy and physics in Europe beyond what the ancients had achieved, was a major factor in bringing the Renaissance to a close. Francis Bacon understood what was happening. He captured these developments in an image which compares voyages of the mind with voyages by ship. The Mediterranean Sea was the boundary of the ancient world, beyond the pillars of Hercules was the unknown Atlantic Ocean. Bacon saw Europeans breaking the bounds of ancient learning and sailing past the Pillars of Hercules (The Straits of Gibralter) and passing out into a voyage of discovery on the unknown sea. Descartes was a great captain in these new intellectual voyages of discovery.


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