Exercise your brain!

Several Thought Experiments



William James’ squirrel:


SOME YEARS AGO, being with a camping party in the mountains, I returned from a solitary ramble to find every one engaged in a ferocious metaphysical dispute. The corpus of the dispute was a squirrel – a live squirrel supposed to be clinging to one side of a tree-trunk; while over against the tree’s opposite side a human being was imagined to stand. This human witness tries to get sight of the squirrel by moving rapidly round the tree, but no matter how fast he goes, the squirrel moves as fast in the opposite direction, and always keeps the tree between himself and the man, so that never a glimpse of him is caught. The resultant metaphysical problem now is this: Does the man go round the squirrel or not? He goes round the tree, sure enough, and the squirrel is on the tree; but does he go round the squirrel? [Stop for discussion] In the unlimited leisure of the wilderness, discussion had been worn threadbare. Every one had taken sides, and was obstinate; and the numbers on both sides were even. Each side, when I appeared therefore appealed to me to make it a majority. Mindful of the scholastic adage that whenever you meet a contradiction you must make a distinction, I immediately sought and found one, as follows: “Which party is right,” I said, “depends on what you practically mean by ‘going round’ the squirrel. If you mean passing from the north of him to the east, then to the south, then to the west, and then to the north of him again, obviously the man does go round him, for he occupies these successive positions. But if on the contrary you mean being first in front of him, then on the right of him, then behind him, then on his left, and finally in front again, it is quite as obvious that the man fails to go round him, for by the compensating movements the squirrel makes, he keeps his belly turned towards the man all the time, and his back turned away. Make the distinction, and there is no occasion for any farther dispute. You are both right and both wrong according as you conceive the verb ‘to go round’ in one practical fashion or the other.”

“What is pragmatism?” 1904 lecture [1]

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SS: Descartes


from Descartes’ Dream, by Phillip J. Davis and Reuben Hirsh

THE MODERN WORLD, our world of triumphant rationality, began on November 10, 1619, with a revelation and a nightmare. On that day, in a room in the small Bavarian village of Ulm, Rene Descartes, a Frenchman, twenty-three years old, crawled into a wall stove and, when he was well warmed, had a vision. It was not a vision of God, or of the Mother of God, or of celestial chariots, or of the New Jerusalem. It was a vision of the unification of all science.

The vision was preceded by a state of intense concentration and agitation. Descartes overheated mind caught fire and provided answers to tremendous problems that had been taxing him for weeks. He was possessed by a Genius, and the answers were revealed in a dazzling, unendurable light. Later, in a state of exhaustion, he went to bed and dreamed three dreams that had been predicted by this Genius.

In the first dream he was revolved by a whirlwind and terrified by phantoms. He experienced a constant feeling of falling. He imagined he would be presented with a melon that came from a far-off land. The wind abated and he woke up. His second dream was one of thunderclaps and sparks flying around his room. In the third dream, all was quiet and contemplative. An anthology of poetry lay on the table. He opened it at random and read the verse of Ausonius, “Quod vitae sectabor iter” (What path shall I take in life?). A stranger appeared and quoted him the verse “Est et non” (Yes and no). Descartes wanted to show him where in the anthology it could be found, but the book disappeared and reappeared. He told the man he would show him a better verse beginning “Quod vitae sectabor iter.” At this point the man, the book, and the whole dream dissolved.

Descartes was so bewildered by all this that he began to pray. He assumed his dreams had a supernatural origin. He vowed he would put his life under the protection of the Blessed Virgin and go on a pilgrimage from Venice to Notre Dame de Lorette, traveling by foot and wearing the humblest-looking clothes he could find.

What was the idea that Descartes saw in a burning flash? He tells us that his third dream pointed to no less than the unification and the illumination of the whole of science, even the whole of knowledge, by one and the same method: the method of reason.

Eighteen years would pass before the world would have the details of the grandiose vision and of the “mirabilis sientiae fundamenta”— the foundations of a marvelous science. Such as he was able to give them, they are contained in the celebrated “Discourse on the Method of Properly Guiding the Reason in the Search of Truth in the Sciences.” According to Descartes, his “method” should be applied when knowledge is sought in any scientific field. It consists of (a) accepting only what is so clear in one’s own mind as to exclude any doubt, (b) splitting large difficulties into smaller one, (c) arguing from the simple to the complex, and (d) checking, when one is done.

March 31 is Descartes’ birthday! Happy Birthday.

Go here for a slide show review of his Meditations.

Here is an earlier birthday post.

Read the entry from Stanford Encyclopedia.

Happy Birthday!

descartesPhilosopher and mathematician René Descartes is regarded as the father of modern philosophy for defining a starting point for existence, “I think; therefore I am.”

René Descartes was born was born on March 31, 1596, in La Haye, France.

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