论证的各部分
和研究论证联系最紧密的知识领域是逻辑，就像其他处理复杂事物的领域一样，逻辑有它自己特殊的术语。既然这本书要超越理论，更加实用，我们限定关注在这些术语中，它们将一个论证表示为不同的部分：前提和结论。在前面提到的维诺娜的论证中，前提是“法律禁止老师在公立学校带领学生祷告”还有“维诺娜在她的公立学校教室中带领学生祷告”。结论是“因此，维诺娜违法了”。因此，怀诺呐违法了。”（单词“因此”和类似“于是”、“后果”等同义词经常用来确定结论。在没有使用它们的地方，你通常可以回答这个问题来识别结论，其他的判断支持或强化了哪个判断？）
逻辑学家在评价论证时使用的基本原则见下列表：
1.前提要么是真，要么是假（正确还是错误）。
2.连接前提和结论的推理是有效还是无效。（要成为有效，陈述的结论，仅仅当结论必须在逻辑上从前提而来。）
3.正确的前提加上有效的推理等于合理的论证。
4.不正确的前提或者无效的推理都意味着论证是不合理的。
在逻辑思考中的错误和在数学中一样常见。不仅仅其他人的思考如此，我们自己也一样。就像我们有精确的数字，尽最大努力认真计算还是会得到错误答案，一样，我们可能从精确的信息得到错误的结论。当然，当我们从不准确的、不完备的、信息开始或者随意推理，错误的机会就更多了。这有一个有趣的（和幽默的）随意推理的案例：一位工人因为长期迟到被解雇后，他的律师争辩说，因为没有要求他戴手表，管理者有过失。
对于观点和推理过程不恰当的态度也会在论证中带来错误。例如，如果你最初认为自己第一印象是正确的，你就可能会不理性地坚持它们，寻找证据支持它们，拒绝不利的证据，并且狂热地进行辩护。这样的方法会让你非常容易陷入自我欺骗中，或者被别人操纵。相反，如果你尝试性的对待自己的第一印象——有趣的可能性而不是确定——并且在形成你的观念前和其他的想法进行对比，你就不大可能自我欺骗或被他人蒙骗。
原文：
The Parts of an Argument
The field of knowledge most closely associated with the study of argument is logic, which, like other fields that deal with complex matters, has its own special terminology. Since this book is more practical than theoretical, we will limit our concern to those terms that signify the parts of an argument: the premises and the conclusion. In the argument about Wynona mentioned above, the premises are “The law prohibits teachers from leading class prayers in public schools” and “Wynona leads students in prayer in her public school classroom.” The conclusion is “Therefore, Wynona is breaking the law.” (The word therefore and synonyms such as so and consequently are often used to identify conclusions. Where they are not used, you can usually identify the conclusion by answering the question, Which assertion do the other assertions support or reinforce?)
The basic principles logicians use in evaluating arguments are as follows:
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The premises are either true or false (correct or incorrect).
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The reasoning that links the premises to the conclusion is either valid or invalid. (To be valid, the stated conclusion, and only that conclusion, must follow logically from the premises.)
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Correct premises plus valid reasoning equal a sound argument.
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Either an incorrect premise or invalid reasoning will render an argument unsound.
Mistakes are as common in logical thinking as they are in mathematics. This is true not only of other people’s thinking but of our own as well. Just as we can have accurate numbers and do our best to add carefully yet come up with the wrong answer, so, too, can we proceed from accurate information to a wrong conclusion. Of course, when we start with inaccurate or incomplete information or reason recklessly, the chances of error are compounded. Here is an interesting (and humorous) example of reckless reasoning: After a worker was fired for being habitually late, his attorney argued that the supervisor was at fault for not demanding that the man wear a watch!1
Inappropriate attitudes toward ideas and the reasoning process can also lead to errors in argument. For example, if you regard your first impressions as infallible, you are likely to embrace them uncritically, seek out evidence that supports them and reject evidence that challenges them, and defend them rabidly. Such an approach leaves you vulnerable both to self-deception and to manipulation by others. In contrast, if you regard your first impressions tentatively—as interesting possibilities rather than certainties—and compare them to other ideas before making up your mind, you are less likely to fool yourself or be deceived by others.
*The only exception to this is pure coincidence. Consider this argument: “Fair-skinned people are more susceptible to skin cancer than dark-skinned people. Florida has more fair-skinned people than Michigan. Therefore, the skin cancer rate is higher in Florida than in Michigan.” The argument is defective because the second premise lacks a basis in fact. Yet the conclusion happens, coincidentally, to be true.
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