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# Validity, Soundness, Strength and Cogency?

Fri 6 Mar, 2009 03:18 am
I gather that validity and soundness apply to deductive arguments, and that strength and cogency apply to inductive arguments, but little more. Could someone please provide me with official definitions and/or personal explanations?
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Type: Question • Score: 0 • Views: 4,805 • Replies: 14

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fresco

3
Fri 6 Mar, 2009 10:41 am
@aperson,
http://www.iep.utm.edu/d/ded-ind.htm
aperson

1
Fri 6 Mar, 2009 06:20 pm
@fresco,
Thanks.
0 Replies

aperson

1
Fri 6 Mar, 2009 07:53 pm
(1) Tony is a ferocious tiger.
(2) Clinton is a lame duck.
Despite their apparent similarity, only (1) has the form "x is a A that is F". From it one can validly infer that Tony is a tiger. One cannot validly infer from (2) that Clinton is a duck.

Could someone please explain this to me?
fresco

2
Sat 7 Mar, 2009 02:49 am
@aperson,
You are confusing what Chomsky called "surface structure" and "deep structure".
"Statements" are only the surface realization of "meaning". Logic only works on the mathematical form i.e. "surface structure" without considering "social context". The word "is" is taken by logic to be equivalent to "is a member of the set of". Logic makes no distinction between "ducks" and "lame ducks" except in the assumption that the latter is a subset of the former. But the deep structure denies that... i.e. in human parlance "lame ducks" are not contextually a subset of "ducks"
fresco

1
Sat 7 Mar, 2009 03:14 am
@fresco,
It may also be of interest that your point reflects Wittgenstein's attack on many philosophical arguments as "language going on holiday". For example to assume that "have a thought" is in some sense similar to "have a pain" or "have a book" can lead to word salad. in general this points to the limitations of traditional logic and goes some way to explaining why Wittgenstein rejected his earlier work on that subject.
aperson

1
Sat 7 Mar, 2009 09:05 pm
@fresco,
I don't want to contridict you, but I'm fairly sure that logic does take into account the "deep" or "contextually relevant" meaning of the word. At least, that's what my lecturer tells us. After all, logic would be quite useless practically if it didn't.
fresco

1
Sun 8 Mar, 2009 02:02 am
@aperson,
I suggest your Logician is overselling his goods. Ask him how static set theory can be applied to a dynamic universe with probabalistic shifting set membership.

Quote:
“The opposite of a correct statement is a false statement. But the opposite of a profound truth may well be another profound truth.”

Niels Bohr.
aperson

1
Mon 9 Mar, 2009 02:37 am
@fresco,
She, actually. What I'm trying to say is that it's not as if common sense can't be applied to logic (in which you seemingly have little faith, why so?). No need to get so caught up in bureacracy and semantics that it loses applicability.

By the way, do you know why context does affect strength in inductive arguments, although it does not affect validity in deductive arguments.
fresco

1
Mon 9 Mar, 2009 08:36 am
@aperson,
Deductive logic reflects mathematical set theory where there are no probabilities involved with set membership. Inductive logic on the other hand assumes common context to establish probabilities of set membership.

The reasons for taking traditional "logic" with a pinch of salt are:
1. It is the assumption of commonality (mutual semantic fields) which Wittgenstein points out to be ill founded in many "philosophical arguments".
In non-philosophical discourse, commonality is often subject to social negotiation not matters of fact.
2. Logic is a product of "human consciousness" and cannot of itself be used to explain "thinking" or "meaning". Indeed Piaget pointed out that "logical thought" itself needs explaining, and does not even occur in all adult humans.
3. Quantum theory in physics indicates that traditional logic cannot be applied to particle phenomena such as "complementarity" which usurps "the law of the excluded middle". Limited attempts have been made to redeem the situation using "multi-valued" and "fuzzy" logic, in which "traditional logic" might be relegated to a restricted case.
http://en.wikipedia.org/wiki/Is_logic_empirical??action=history
aperson

1
Mon 9 Mar, 2009 09:36 pm
@fresco,
Sorry, you're going to have to dumb that down a bit for me here. I still don't really understand.

I'm going to swallow and pride and tell you that I often find you quite difficult to understand, fresco. I'm only sixteen; I don't know what "mutual semantics fields", "commonality" or "the law of the excluded middle" are, or who Wittgenstein and Piaget are. Please excuse me if this frustrates you, I understand.

I think I get the gist of what you are saying, though.
2. Although logic is only logical from our perception (this is what you are saying, right?), I think we only try to make sense of the world from our perception. Everything we know is from our perception. Indeed, I don't believe the "true" natures of the universe are knowable to us, for one because in order for an intelligent being to observe something, in must first be skewed and filtered to be observable. Everything must be viewed from some sort of incorrect or morphed perception.
3. Logic generally doesn't deal with sub-atomic particles; although nothing is certain (ignoring issues of certainty) on a quantum scale, things can be certain on our scale (correct me if I'm wrong).
fresco

1
Tue 10 Mar, 2009 08:01 am
@aperson,
My apologies for the complexity.

You are correct about the fact that perception as active not passive. It is we who "segment reality" by use of language. There are no "objective properties of objects", only our expectancies of our relationships with the world couched in mutual descriptions according to common needs. (Hence my terms "commonality" and " mutual semantic fields") From this point of view "logic" is merely a secondary tool for "thinking". If you look up Godel's incompleteness theorem you will find that all systems contain at least one axiom whose "truth" is assumed from outside the system. This means that "logical validity" and "truth" are ultimately different ball games.

I hope this is sufficient to explain my position.
aperson

1
Tue 10 Mar, 2009 06:02 pm
@fresco,
Ok, I get you now, but as I said, we generally don't need to find real "truth", only local "truth".
fresco

1
Wed 11 Mar, 2009 12:37 am
@aperson,
Indeed ! There may only be "local truth" !
aperson

1
Fri 13 Mar, 2009 01:27 am
@fresco,
An interesting concept, but of course we cannot know.
0 Replies

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