Changing scopes:偷换范围

The fact that ...could sufficiently substantiate the conclusion that...since the argument is based only on (some special cases) and the author does not differentiate between the ...of (different subjects) .Although the author’s inference that ...might be true for some cases, for example, ...Unfortunately, this is not true of every individual (in the general group). (other subjects may have totally different situation thus the author’s inference could not be properly applied to them. ) Unless the author can demonstrate that (the condition of other subjects is similar to that of the case studied), the general conclusion cannot be reached merely basing on these special and limited cases.

Inferring a future condition from a past condition:过去不能推未来

In the argument the author suggests that we can (solve current problems or achieve current goals) through methods which have successfully solved the same kind of problems in the past.There is a hidden assumption assumed by the author that all conditions and factors upon which the effectiveness of (the method) depend have remained unchanged during the past (N years).However, many factors could have been changed during the past years. (many conditions and factors could have varied, which might render the solutions which were proved to be effective in the past might not have the same effectiveness in current days or in the future. )Without taking into account all these constantly changing factors, the author could not convince us that the proposed solution could be used to solve current problems successfully.