The author falsely depends on gratuitous assumption that.... However, no evidence is stated in the argument to support this assumption. In fact, this is not necessarily the case. For example, it is more likely that.... Therefore, this argument is unwarranted without ruling out such possibility.
以次类推,我们可以写出同样思路但是不同表述的句子. 比如
The author illogically relies on the groundless assumption that ... .
The author erroneously depends on the unwarranted presumption that ... .
如果可以,大家也可以尝试一下改变句式. 比如
The author commits a fallacy of ... in assuming that .... .
The arugment is based on a gratuitous assumption that ... .
举例可以用for example, for instance, It's possible that ... 等等.