On the utility of changing arguments, hypothetical arguments and the rest

Epictetus – Discourses Book 1
I.7. On the utility of changing arguments, hypothetical arguments and the rest

If you want to walk the path of the philosopher, you must learn how to logically differentiate true from false. You have to be able to distinguish a valid argument from fallacies and sophistry.

Therefore you must learn the rules of consequence to know how conclusions follow premises:

1. When considering an argument be careful that the premises you have admitted are not changed when the conclusion is reached.
2. Put differently, you should not accept conclusions that change their premises.
3. But if the premises are not changed and you have admitted them, you have the obligation to accept what flows from them.

The same goes for hypotheses and hypothetical arguments:

1. Once you grant an hypothesis, you should accept only what is consistent with it, and reject what is in conflict.
2. You cannot grant an hypothesis and then accept another that is conflict with the latter.

Learning and knowing these rules are crucial to tell valid proof from fallacy.