Argument 1

Premise: Human can find some ways to get knowledge.

Conclusion: People cannot know anything to be true.

Attack: In the premise, the man believes that human can find the truth finally although they need to search from the position of skepticism.However, the man thinks that people have no way to know anything true, people cannot know anything to judge true or false.

Argument 2

Premise: Each individual needs to determine what’s right from an objective fact which is confirmed by a large number of evidences.

Conclusion: “My” opinion that “smoking marijuana doesn’t unethical” is right.

Attack: From the premise, the man thinks that everyone can have their own view on smoking marijuana but in conclusion, the man believes that he himself is right only. Obviously, his conclusion just sets up when he is “right” and it’s subjective thought but not the fact when people read it.