用逆否命题检验推理方向？ 请指教

guoqi

麻烦问下大家，就是lawyer大神曾经贴出来的一个题
No mathematical proposition can be proven true by observation. It follows that it is impossible to know any mathematical proposition to be true.
在这个题里面，lawyer 指出用 选项的逆否命题的方式去检验是否该选项推理方向是否跟原命题一致？ 不太明白 第一次见这种方法，请大家说说这种方式的原理

guoqi

顶一下

sdcar2010

Premise: If mathematical proposition, then cannot be proven true by observation.

Conclusion: If mathematical proposition, then one cannot know the proposition is true.

Assumption: If something cannot be proven true by observation, then one cannot know the proposition is true. Or to know something is true, one has to prove it true by observation. These two statements are contrapositive pairs.