Using Argument as a Tool of Criticism

In a valid argument true premisses will never lead you to a false conclusion as the definition of a valid argument states that, whether the premisses are in fact true or false, if its premisses were true, then the conclusion must also be true. This means that if the conclusion of a valid argument is false, then at least one of the premisses must be false. Truth is transmitted from the premisses of a valid argument to the conclusion; falsity is re-transmitted back to the premisses.

Category:

Education

Tags:

• valid
• argument
• logic
• deduction
• inference

[osheaad]

1) All birds have feathers; there is no animal with feathers that is not a bird.

2) There are animals with feathers that cannot fly, being too heavy.

3) An ostrich is a feathered animal that cannot fly, being too heavy.

_______________

4) Therefore NOT all birds can fly.

[NaiveRealist]

Dear osheaad,

Nice argument. Duhem's point comes to the for here. Duhem pointed out that in trying to refute a hypothesis, we draw out conclusions from a number of premises using a valid argument. If the conclusion is false, then we can reason "back" to the premises, drawing the conclusion that the premises must be false. However, we do not know which premise is at fault. The definition of a valid argument tells us is that if the conclusion is false, then at least one premise must be false.

[DoCWaSaBe]

1-all birds can fly

2-penguins cant fly

penguins are not birds

is that how you do disprove the first premise? assuming we know penguins cant fly and that there birds

[NaiveRealist]

@DoCWaSaBe

Sorry to have taken forever to reply! Well, to refute the the universal statement that all birds can fly, one needs just one counterexample - a bird that can't fly. The argument would be a Modus Tollens: If P, then Q; but we have P and not Q; therefore= not (If P, then Q). "P" stands for "is a bird" and "Q" stands for "can fly". In my example, I'm just taking only the information in the argument, ignoring what we think we know about birds or penguins etc.

[NaiveRealist]

Part 1

Thanks for the comment. You say "bad" argument. Well, in the video I was making the distinction between questions to do with whether the premisses or conclusion are true and whether the argument is well put together - whether it is "valid". The thing is, you can evaluate an argument in 2 ways: 1. does it have the right form (is it valid) and 2. are its premisses and conclusion true.

[jedivolks]

i'm taking an intro to philosophy class and i am stumped on valid and invalid arguments. How can a bad argument be valid? how do you know if it's structure is well put together? And can you also explain to me a deductive proof? I wish to know what you do...