Logic vs Evidence

[BrianSoddingBoru4]

Perhaps we are missing Dimaniac's question entirely.

Can a conclusion both sound and valid contradict reality?

Of course it can. If the premises are false then the conclusion is false, but can be bother logically sound. It is important to remember that in logic, 'sound' only means that the conclusion does not contradict the premises - 'sound' isn't the same as 'true'. This is the classic example:

P1. Socrates was a mammal.
P2. All mammals are cats.
C. Socrates was a cat.

Here, the problem is with P2. Thus the conclusion ('Socrates was a cat') is sound, as it follows necessarily from the premises. However, since premise 2 is demonstrable false (not all mammals are cats), the conclusion cannot be true.

Boru

[jgnat]

Responding to Fidel Castronaut, you make my point very well. An expert may evaluate textual evidence based on conventions and markers, but a celestial sighting or geological record (strata) will always trump the text. Geological strata would have recorded a world-wide flood.

[Mystic]

Depending on how you define logic, logic includes things like belief in a sense of self (that minute ago you, is the same you), belief in other minds, belief things weren't just created a few seconds ago with false appearance of age and false memory, belief in induction and other things.

The fact we have properly basic beliefs on logic doesn't give you the go ahead to believe whatever you want and say it's properly basic though.

However, whether objective morality exists or God exists, stuff like that, can be argued either way.

There are some people who don't believe the physical world exists.

---

Perhaps we are missing Dimaniac's question entirely.

Can a conclusion both sound and valid contradict reality?

Of course it can. If the premises are false then the conclusion is false, but can be bother logically sound. It is important to remember that in logic, 'sound' only means that the conclusion does not contradict the premises - 'sound' isn't the same as 'true'. This is the classic example:

P1. Socrates was a mammal.
P2. All mammals are cats.
C. Socrates was a cat.

Here, the problem is with P2. Thus the conclusion ('Socrates was a cat') is sound, as it follows necessarily from the premises. However, since premise 2 is demonstrable false (not all mammals are cats), the conclusion cannot be true.

Boru

Sound means premises are true and the argument is valid. Rationally, it's impossible for the conclusion not to be true.

[Alex K]

Perhaps we are missing Dimaniac's question entirely.

Can a conclusion both sound and valid contradict reality?

Of course it can. If the premises are false then the conclusion is false, but can be bother logically sound. It is important to remember that in logic, 'sound' only means that the conclusion does not contradict the premises - 'sound' isn't the same as 'true'. This is the classic example:

P1. Socrates was a mammal.
P2. All mammals are cats.
C. Socrates was a cat.

Here, the problem is with P2. Thus the conclusion ('Socrates was a cat') is sound, as it follows necessarily from the premises. However, since premise 2 is demonstrable false (not all mammals are cats), the conclusion cannot be true.

Boru

Formally, the relation A=>B always yields "True" when A is false.

[Fidel_Castronaut]

Responding to Fidel Castronaut, you make my point very well. An expert may evaluate textual evidence based on conventions and markers, but a celestial sighting or geological record (strata) will always trump the text. Geological strata would have recorded a world-wide flood.

Quite so!

[Cato]

Perhaps we are missing Dimaniac's question entirely.

Can a conclusion both sound and valid contradict reality?

Of course it can. If the premises are false then the conclusion is false, but can be bother logically sound. It is important to remember that in logic, 'sound' only means that the conclusion does not contradict the premises - 'sound' isn't the same as 'true'. This is the classic example:

P1. Socrates was a mammal.
P2. All mammals are cats.
C. Socrates was a cat.

Here, the problem is with P2. Thus the conclusion ('Socrates was a cat') is sound, as it follows necessarily from the premises. However, since premise 2 is demonstrable false (not all mammals are cats), the conclusion cannot be true.

Boru

I think you're confusing sound and valid. The above is a valid argument since C is true if the premises are true, but unsound because P2 is not true. Also, since it is unsound it does not meet TreeSapNest's criteria.

I am trying to think of an example, but don't immediately think that arguments that are both sound and valid can contradict reality. Mostly, because reality is the arbiter of the truthfulness of premises.

[genkaus]

Of course it can. If the premises are false then the conclusion is false, but can be bother logically sound. It is important to remember that in logic, 'sound' only means that the conclusion does not contradict the premises - 'sound' isn't the same as 'true'. This is the classic example:

P1. Socrates was a mammal.
P2. All mammals are cats.
C. Socrates was a cat.

Here, the problem is with P2. Thus the conclusion ('Socrates was a cat') is sound, as it follows necessarily from the premises. However, since premise 2 is demonstrable false (not all mammals are cats), the conclusion cannot be true.

Boru

You are confusing soundness and validity

An argument is sound if and only if

The argument is valid.
All of its premises are true.

Here, P2 is false which makes the argument valid but unsound.

Edit: I see Cato beat me to it.

[TreeSapNest]

I am trying to think of an example, but don't immediately think that arguments that are both sound and valid can contradict reality. Mostly, because reality is the arbiter of the truthfulness of premises.

I agree. So the answer would seem to force us to examine validity, logic itself. X strictly implies Y, for example. I don't know formal logic well enough to make that examination. :-)

Logic to me is semantic. A definitional truth.

All mammals breast feed.
Humans breast feed.
Humans are mammals.

I forget the axiom involved, but something to the effect of A is A.

[Whateverist]

The smart money says evidence takes logic in five rounds.

[dyresand]

Can these things potentially contradict each other?

logic and evidence are the same side of the coin.
it would be like asking what what does air taste like.
evidence for a god does not exist and the bible isn't
solid evidence. if there was solid evidence for a god
it would be common knowledge and atheists would
not exist.