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哲学趣谈之演绎逻辑 Deductive Logic

 美式发音 适合泛听

亚里斯多德

 Deductive logic reasons from the general to the particular. The 2)bare-bones deductive argument is the 3)syllogism, “All men are mortal, Socrates is a man, therefore Socrates is a mortal.”
  It’s amazing how often people screw this up and argue something like, “All men are mortal, Soctates is mortal, therefore Socrates is a man,” which doesn’t logically follow. That would be like saying, “All men are mortal, my kid’s 4)hamster is mortal, therefore my kid’s hamster is a man.”
  Another way to screw up a deductive argument is by arguing from a false 5)premise.
  An old cowboy goes into a bar and orders a drink. As he sits there 6)sipping his whiskey, a young lady sits down next to him. She turns to the cowboy and asks him, “Are you a real cowboy?” He replies, “Well, I spent my whole life on the 7)ranch, herdin’ horses, mendin’ fences and brandin’ cattle, so I guess I am.” She says, “I’m a lesbian. I spend my whole day thinkin’ about women. As soon as I get up in the morning, I think about women. When I shower or watch TV, everything seems to make me think of women.” A little while later a couple sits down next to the old cowboy and asks him, “Are you a real cowboy?” He replies, “Well, I always thought I was, but I just found out I’m a lesbian.”
  Perhaps it would be fun to analyze exactly where the cowboy went wrong. Perhaps not. But we’re going to do it anyhow. In his first answer to the question of whether he’s a real cowboy, he reasoned, (1) If someone spends all his time doing cowboy type things, he’s a real cowboy. (2) I spend all my time doing those cowboy type things, (3) therefore, I’m a real cowboy.
  The woman reasoned, (1) If a woman spends all her time thinking about women, she’s a lesbian. (2) I’m a woman. (3) I spend all my time thinking about women, (4) therefore I am a lesbian.
  When the cowboy then reasons to the same conclusion, he assumes a premise that, in his case, is false, namely (2) I am a woman.
  OK, we never promised you that philosophy is the same as jokes.
  
  演绎逻辑是一种从一般到特殊的逻辑推理方法。基本的演绎论证是三段论:“所有的人都终有一死,苏格拉底是个人,因此苏格拉底终有一死。”
  而令人吃惊的是,人们常常将其弄得一团糟,为诸如此类的话题争辩:“所有的人都终有一死,苏格拉底终有一死,因此苏格拉底是个人。”从逻辑上讲并不能得出这样的结论。这就像是说:“所有的人都终有一死,我家孩子养的仓鼠终有一死,因此我家孩子养的仓鼠是个人。”
  另一种乱用演绎论证的方式是从一个错误的前提进行论证。
  一位老牛仔走进了一间酒吧,点了一杯酒。当他坐在那里小口呷着他的威士忌时,一位年轻的女士在他旁边坐下了。她转向这位老牛仔问道:“你真的是一位牛仔吗?”他回答道:“嗯,我一辈子都是在牧场度过,牧马、修补篱笆、给牲口打烙印,所以我想我是个牛仔。”她说道:“我是个女同性恋。我整天都在想着女人。当我早上起床后,我想着女人。当我洗澡或看电视时,每一件事情似乎都让我想到女人。”过了一会儿,一对夫妇坐在老牛仔旁边,问他道:“你真的是一位牛仔吗?”他回答道,“嗯,我一直认为我是的,但我刚发现原来我是个女同性恋。”
  要准确地分析出这位牛仔错在哪里,或许是件有趣的事情,又或许不是。但我们还是要分析一番。当他第一次回答关于他是不是一位真正的牛仔的问题时,他推理说:(1)如果某人所有的时间都在做牛仔该做的事情,那么他是一位真正的牛仔。(2)我所有的时间都用在做牛仔该做的事情上了。(3)因此,我是一位真正的牛仔。
  那位女士推理说:(1)如果一个女人所有的时间都在想着女人,她就是个女同性恋。(2)我是个女人。(3)我所有的时间都在想着女人。(4)因此,我是个女同性恋。
  接着当这位牛仔推理出相同的结论时,他假设了一个前提,而这个前提在他的推理中是错误的,亦即,(2)我是个女人。
  好了,我们可从未向你许诺说:哲学和笑话是一回事。
  
  翻译:小狐

1)      deductive [dI5dQktIv] a. 推论的,演绎的
2)      bare-bones a. 基本的
3)      syllogism [5sIlEdVIzEm] n. 三段论
4)      hamster [5hAmstE] n. 仓鼠
5)      premise [5premIs] n. 前提
6)      sip [sIp] v. 小口喝,呷
7)      ranch [rB:ntF] n. 大农场,大牧场


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