Logic vs Evidence

[Chas]

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.

Your syllogism is, in fact, incorrect.

An equivalent syllogism:
All prime numbers greater than two are odd.
Nine is an odd number.
Nine is a prime number.

[dyresand]

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.

Your syllogism is, in fact, incorrect.

An equivalent syllogism:
All prime numbers greater than two are odd.
Nine is an odd number.
Nine is a prime number.

sun goes up
sun goes down
reality
we revolve around the sun giving the illusion that the sun is moving up and down.

[Lao Shizi]

"Deduction: In the process of deduction, you begin with some statements, called 'premises', that are assumed to be true, you then determine what else would have to be true if the premises are true. For example, you can begin by assuming that God exists, and is good, and then determine what would logically follow from such an assumption. You can begin by assuming that if you think, then you must exist, and work from there. In mathematics you can begin with some axioms and then determine what you can prove to be true given those axioms. With deduction you can provide absolute proof of your conclusions, given that your premises are correct. The premises themselves, however, remain unproven and unprovable, they must be accepted on face value, or by faith, or for the purpose of exploration.

Induction: In the process of induction, you begin with some data, and then determine what general conclusion(s) can logically be derived from those data. In other words, you determine what theory or theories could explain the data. For example, you note that the probability of becoming schizophrenic is greatly increased if at least one parent is schizophrenic, and from that you conclude that schizophrenia may be inherited. That is certainly a reasonable hypothesis given the data. Note, however, that induction does not prove that the theory is correct. There are often alternative theories that are also supported by the data. For example, the behavior of the schizophrenic parent may cause the child to be schizophrenic, not the genes. What is important in induction is that the theory does indeed offer a logical explanation of the data. To conclude that the parents have no effect on the schizophrenia of the children is not supportable given the data, and would not be a logical conclusion."

[Mequa]

In my view, inductive reasoning is far more important than deductive logic (the old Medieval scholastic/neo-Aristotelian approach) when it comes to interpreting empirical data. All of empirical science is rooted in it.

[bennyboy]

What's this "vs" bullshit? Surely one of the rules of logic is that if you are making assertions about reality, you need to be able to demonstrate that they actually represent reality.