1. 什么是推理？

推理是应用实例（论据）得出结论（论点）的过程。作者可能举出一个或数个相关的证据，附之理由，最后推出一个正确（或者可能正确）的结论。

下面这篇短文就包含推理:

New evidence shows that the AIDS virus may not be as lethal as it has been thought to be and that some people may be able to develop a defense against it. The evidence involves an appreciable number of people who have been HIV positive for many years (some of them for twelve years or more). Lab tests show that the virus is present in their blood. But they have not developed any symptoms of AIDS. They continue to be in good health and show no signs of developing the disease. Some researchers estimate that as many as 5% of those infected by the virus may be in this category and that they will never develop the disease.

 这里，作者做出了艾滋病病毒到底有多致命的论述：也许，艾滋病毒并非100%致命。有些人能抵抗这种病毒，或许是因为自然免疫力。然后，作者举出实例/事实来证明这个论述是正确的：有些人很多年以前就感染了艾滋病毒但却根本就没有扩张的迹象。我们可以这么认为，写这篇文章的作者引用这个事实来证明他关于艾滋病毒有多致命的论点。

2. 前提（Premises）和结论（Conclusions）

     在这个推理中，作者用一些论述来支持其它的论述。被支持的论述称为结论，而用以支持的论述则为前提。在一个推理中，或许会有一个以上的结论和多个前提。在这段关于艾滋病的推理中就有一系列相互联系的结论：

New evidence shows that the AIDS virus may not be as lethal as it has been thought to be and that some people may be able to develop a defense against it.

     在支持这些结论时，作者引用了这样的事实：很多人在就感染了艾滋病毒，但却没有得病的迹象。后面那一句就是前提。

     怎样识别前提和结论呢？可靠的线索经常由一些关键词引出，而我们可以利用这些关键词来识别前提和结论。以下这些词经常用来引出结论：

So...
This shows that...
Therefore...
We can infer that...
Hence...
Consequently...
It follows that...
This indicates that...
For that reason, we may say...

而下面这些词则引出推理的前提：

The reason is that...
Because...
Since...
Evidence...
On the basis of...
It follows from...
In view of...
We may infer from...

       一旦你能分辨出哪些是前提而哪些是结论，你就很容易分析前提是否有效地支持结论。在很多逻辑推理题中，前提和结论中间存在着一个gap，即假设。你所做的是找出这个gap（假设），然后用它来回答后面的问题。如上面的那个关于艾滋病的推理，其中的一个未阐述的假设是“关于艾滋病范者的数据是正确的”。总的说来，逻辑推理的方程式是这样的：

Premises + Assumptions = Conclusion

3. 三段论思维---寻找假设的最佳方法

什么是三段论？韦氏字典里面的解析是这样的: Every virtue is laudable; kindness is a virtue; therefore, kindness is laudable。用最简单的表达方式就是：如果A→B ，而且B→C，那么A→C。