Forums → WEPR → Arguments of logic

however a logically sound argument does not require true premises and conclusions

Not to pick (and this thread will probably be locked anyway) but a logically sound argument does require true premises.
A valid argument is one in which it is impossible to have true premises and a false conclusion. A sound argument is an argument that is a) valid and b) has true premises. Note, since the argument is valid and sound, that implies the conclusion will be true.

But so far, I have seen even a logically valid argument on this thread yet, so I'm not even sure it's achieving its goal of using logic

Not to pick (and this thread will probably be locked anyway) but a logically sound argument does require true premises.
A valid argument is one in which it is impossible to have true premises and a false conclusion. A sound argument is an argument that is a) valid and b) has true premises. Note, since the argument is valid and sound, that implies the conclusion will be true.

Thanks for the correction Moe, I have a relatively limited knowledge on the finer points of logic, especially the accompanying vernacular.

...ok, I did misread it, but please explain how the sky is blue because of water. Water vapour is not the only thing in the air (i.e. oxygen, varios carbons, ozone, etc)

Those are the components of dry air, which I stated to be clear.

But so far, I have seen even a logically valid argument on this thread yet, so I'm not even sure it's achieving its goal of using logic

My argument was sound and logical while at the same time disproving another's claim.

My argument was sound and logical while at the same time disproving another's claim.

Here's your argument, from page 1:

Water is blue.
The sky is blue.
Dry air is clear.
Air contains water vapor.
Ergo, the sky is blue due to the presence of water.


You say your argument is logical, although I'm not sure what you mean by that. But if your claim is that your argument is valid, it certainly isn't. It is certainly possible for the premises of your argument to be true and the conclusion false (in fact, the premises say nothing about the presence of substances generating color).

To see this, I can present an analogue of your argument:

This crayon is blue.
This marker is blue.
This sharpie is black.
A crayon box contains this crayon.
Therefore, a crayon box is blue because of the presence of this crayon.

And, since the argument is not valid, it is also unsound.

But since we're talking about scientific-type stuff and empirical observations, I thought I might revive this thread by posing a question about the rigors of science.
Suppose we wanted to prove a universal statement like "All ravens are black." Unfortunately, the intro to logic thread I have doesn't teach this kind of logic, but the formula would look kinda like:

(Ax)(Rx -> Bx) : For any x, if x is a raven, then x is black.
This is equivalent to:
~(Ex)(Rx ^ ~Bx) : There does not exist an x such that x is a raven and x is not black.
*Note: the (Ax) and (Ex) are quantifiers and don't actually look like this. The 'A' is upside down and the 'E' is backwards. The former is a universal quantifier and the latter is an existential quantifier, if anyone cares.

So, how do we prove this statement? In other words, can we verify it?
What I'm really interested in is this other logical equivalence:

(Ax)(~Bx -. Rx) : For any x, if x is not black, then x is not a raven.

Now, logically, this means the same things as the first statement. But the first would have us look at every raven in existence to see if it's black. The second would have us look at every non-black thing to make sure it's not a raven. Does this seem right? Is this what we end up proving?
There's a lot to be said here, but I'll let you guys do the talking.

Water is blue.
The sky is blue.
Dry air is clear.
Air contains water vapor.
Ergo, the sky is blue due to the presence of water.

Accept when the sky is orange, or red, or green, or purple... Wait yet there is still water present.