Can someone help me understand if this argument is valid or not and why or why not?

Question

I'll first admit that this is homework, but I am not just looking for an answer, as I want to understand how to determine if the argument is considered valid, and why.

If an alien spaceship has landed, there should be a large circular depression in the field.

There is a large circular depression in the field. So the alien spaceship must have landed.

Now I know that when dealing with the "assumption words" (should and must), then it is said to be invalid, but then I get confused with deductive and inductive and don't know if they are the same as valid and invalid, and according to the book, I am looking to see if the argument is valid.

If any philosophy buffs really love your stuff, then please have a go at this...

Thanks

Answer 1

It is invalid unless the following can also be included: The only thing that can cause a large circular depression in a field is an alien spaceship.

Since this statement has not been stated, then it is possible that something else caused the large circular depression in the field.

Answer 2

You are on the right track.

"The large circular depression" is a bias. This is an assumption based on information that is not factual such as assuming that spacecraft must be round and must leave a depression. There could be other type of craft like the Mars landers that bounce, have jets, or landing gear and that have a variety of shapes.

Or, when you start with a false premise, the conclusion that results is often false.

The reasoning must take into account other rational and reasonable explanations for a circular depression. Or, you look at the opening premise for any argument an determine that it is "not always true". (Most of us will consider something true or false, rather than how how often the premise is true.)

Instead of "So" an alien spaceship must have landed, you can also try "therefore". The SO or the THEREFORE is where you are drawing a conclusion from your original premise.

False premise leads to a false conclusion which can be disputed.

Answer 3

You can test the argument by substituting different nouns, e.g

If the cat(=spaceship) landed on the fishbowl (=in the field), there should ((Whoops-first danger signal--too indefinite to be in a syllogism)) be water on the floor (=circular depression). There is water on the floor, so (therefore) the cat landed on the fishbowl.

Well, the water could get on the floor in several other ways, and it is possible that the cat could land on the fishbowl and scoop up the fish without getting water on the floor.
Therefore the argument is twice invalid. And no, in this case two negatives do not make a positive.

Answer 4

If you took an introductory course in philosophy, do you remember: "All dogs have four legs, therefore all animals with four legs are dogs"?

You've started with an incorrect definition.
1. Neither statements are "arguments;" they are false premises--assumptions. (An opinion is not a debate.)
Logical reasoning tells us:
a) We don't know if there are alien spaceships
b) We then can't speculate on their shape
c) "They" might not even leave depressions
d) We see a circular depression
e) We don't know what caused it
The connection between spaceships & circular depressions is drawn by a false assumption.

"Thererfore" is an adverb>"for that reason." Since there is no logical reasoning in the conclusion, the word is inappropriate.
(As shown in the dog statement.)

Answer 5

That phrase reminds me of a question asked by a professor in college. There is a tree in the forest and no one is around, if the tree falls does it make a sound?

gatita_63109

Answer 6

hghghghghg ?