## Introduction to Logic - Deductive and Inductive Arguments

• Posted by a hidden member.
From another thread, it is clear that statements are made without any logic to back them up. Possibly one of the divides in many of the political arguments is some look to logic to support their points, while others do not, either because they don't understand logic, consider it irrelevant, or lack the proper discipline to apply logic.

This is not to suggest that every statement needs a logical backup. We have all expressed gut-feel opinions, sometimes relying on emotion, which has its place. The problem exists when someone makes an assertion, disguised as a fact, and bases it on other assertions, often also disguised as facts, and comes to a conclusion based on defective logic. Lose-lose all around. Following thread is presents an example, the posts from today, in particular.
http://www.realjock.com/gayforums/2072577

The following web site presents a description of logic applied to arguments, with numerous examples and some quizzes. Wouldn't it be interesting if a forum required passing the quiz before being allowed to present an argument?

By the way, only brief excerpts from the site are shown here:

http://philosophy.lander.edu/logic/ded_ind.html

I. We have said that the central concern of logic is the evaluation of arguments. In general, for the purposes of this course arguments will fall into two kinds: deductive and inductive. (As noted before there are other kinds of logic not fitting well into either category: e.g., modal logics, logic of commands, some multi-value logics, to name a few.)

II. The Difference between Deduction and Induction

A. Deduction: an argument whose premisses are claimed to provide conclusive evidence for the truth of its conclusion. (This definition is a bit of a kludge since we want to retain a meaning to the phrase "invalid deductive argument" which might be, in some cases, a correct inductive argument.) In the beginning, it's probably best to think of a good or valid deductive argument as one in which the conclusion follows from the premiss(es) with logical necessity.

B. Induction: arguments that establish the truth of the conclusion as probable or probably true. So, informally at least, an inductive argument claims its conclusion follows with some degree of probability. The word "claims" is included in this version of the definition if we want to use the meaningful phrase "incorrect inductive argument."
• Posted by a hidden member.
It has often been of interest to me why the standard of discussion on this board is so lamentable, and spurious logic is certainly a contributing factor. But you haven't been particularly clear about what logic actually *is*, and if you were to do so you would see the real problem.

Logic is a mechanism for deducing the validity or otherwise of propositions given a set of axioms. If the axioms are clearly stated, and they are sufficient to decide the proposition, then anyone familiar with the calculus of logic can agree whether the rules have been applied properly.

It is true that some political debates include fallacies of logic—including, might I add, many that the OP has advocated! They're common and quite easy to spot—ad hominem, ad misericordiam, slippery slope, etc—although a complete taxonomy of formal fallacies has not been offered.

Armed with the knowledge of such fallacies, novices in logic often assume that they have the power to resolve all discord. Their rapid disillusionment is in part due to a technical limitation of logic, namely Godel's incompleteness theorem—no system of axioms can simultaneously be constructed such that all questions are decidable within the system [completeness] and also that the system will yield uniquely uncontradictory results for all questions [consistency]—but more because political debate does not, at its heart, really involve conflicts of logic but rather three much more serious problems:

(i) Non-uniqueness and improvable optimality of axioms—it is not possible to select a unique, optimal set of axioms for political questions, much less is it possible to prove their optimality within the set of chosen axioms. Most political conflict in fact results from different choices of axioms, none of which are provably superior to one another.

(ii) Political problems are typically overconstrained. Worse than (i) seemingly reasonable choices of axiom in seemingly straightforward problems frequently yield no solution at all (see Arrow's impossibility theorem). Toy examples like this show that political questions are actually over-constrained in the sense that one or more of the desiderata must be relaxed to yield a solution. Since there is no way to do this optimally, or to prove optimality, irrational conflict is inevitable.

(iii) Incompleteness of information. In fact, political discussions can very rarely take place in conventional logic at all, relying as they typically do on incomplete information. It is rarely realized the vast epistemological leap required to construct a logical calculus adequate to treat such problems which are rather of *inference* rather than induction or deduction. In practice, most people are using probabilistic logic [see Edwin Jaynes, etc] without realizing it. In this formulation, one's prior "knowledge" about the validity or otherwise of a selection of possible explanations or models is updated by the accumulation of evidence according to Bayes' Theorem. The problem of axioms (i) is now transposed into the problem of assigning prior probabilities—different observers will inevitably have different ones!

I could go on forever, but I've tried to explain why, despite seeming quite promising, correct use of logic is only a partial solution to problems in political discussion. Due to the overwhelming difficulties presented by the strong formulation, I'm a proponent of what I would call "weak" approaches (this is in a very technical, mathematical sense of the word).

What I essentially think is that rather than attempt to debate policy in an overtly holistic sense that is so obviously doomed to failure, we should focus on criteria like Pareto efficiency [policy is Pareto efficient if there is nothing that can be done to make any individual better without making anyone else worse]. It ought to be obvious that most policy is far from Pareto Efficient!

To answer your original point: to be perfectly honest, I don't recall anyone on this board—with the exception of Satyricon331—who really had much of a clue about logic. Alas.
• Posted by a hidden member.
Tim - You realize, of course, that Socal isn't really interested in logic. If so, he couldn't post the kind of nonsensical sources he does on a regular basis.
• Posted by a hidden member.
TigerTim said...To answer your original point: to be perfectly honest, I don't recall anyone on this board—with the exception of Satyricon331—who really had much of a clue about logic. Alas.

Always good to be perfectly honest. Would it be a logical assumption that Mr. Tim, by stating who does have a clue about logic, is including himself in that group by implication, but does not want to explicitly state such out of a very newly acquired humility?
• Posted by a hidden member.
SoCal,
I'm glad I'm not the only one who is feeling the lack of logical discourse in the forums. However, I'm not sure I would place much trust in a site that thinks "premise," a word I think we both would consider a major term in this field, is spelled "premiss."

While it has its own limitations, I'm a fan of this page on logical fallacies. I've occasionally linked to specific sections of it during online arguments with idiots "full of sound and fury, signifying nothing:"

http://www.nizkor.org/features/fallacies/
• Posted by a hidden member.
EliStark saidSoCal,
I'm glad I'm not the only one who is feeling the lack of logical discourse in the forums. However, I'm not sure I would place much trust in a site that thinks "premise," a word I think we both would consider a major term in this field, is spelled "premiss."

While it has its own limitations, I'm a fan of this page on logical fallacies. I've occasionally linked to specific sections of it during online arguments with idiots "full of sound and fury, signifying nothing:"

http://www.nizkor.org/features/fallacies/

Good link. Thanks for sharing. I agree with your spelling, but did a search and at least from the sources that come up on the web showed "premiss" also acceptable, though indicated as an alternate spelling. My Random House Thesaurus only shows "premise", but FWIW, I have a large Oxford English-Russian Dictionary that indicates "premiss" as an alternate British spelling.
• Posted by a hidden member.
socalfitness said
TigerTim said...To answer your original point: to be perfectly honest, I don't recall anyone on this board—with the exception of Satyricon331—who really had much of a clue about logic. Alas.

Always good to be perfectly honest. Would it be a logical assumption that Mr. Tim, by stating who does have a clue about logic, is including himself in that group by implication, but does not want to explicitly state such out of a very newly acquired humility?

How about you respond to the substantive part of my post and not the wistful where is satyricon331 when you need him part?
• Posted by a hidden member.
Christian73 saidTim - You realize, of course, that Socal isn't really interested in logic. If so, he couldn't post the kind of nonsensical sources he does on a regular basis.

Well I think he wants to think he is. Which is sort of laudible, no?
• Posted by a hidden member.
TigerTim said
socalfitness said
TigerTim said...To answer your original point: to be perfectly honest, I don't recall anyone on this board—with the exception of Satyricon331—who really had much of a clue about logic. Alas.

Always good to be perfectly honest. Would it be a logical assumption that Mr. Tim, by stating who does have a clue about logic, is including himself in that group by implication, but does not want to explicitly state such out of a very newly acquired humility?

How about you respond to the substantive part of my post and not the wistful where is satyricon331 when you need him part?

OK - essentially agree. Regarding the incompleteness of information - agree many use probabilistic logic to arrive at a conclusion without realizing it. Furthermore, assumptions are often not defined that are implicit to a conclusion. Qualifying terms such as primarily, or most likely, etc. are avoided, not only to avoid being verbose, but also because it suggests a position is tentative, which is not the case. Also agree on the applicability of the "weak" approach. I would express that in common terms to suggest even if an ironclad rigorously logical argument is not feasible, at least try to present reasonable rationale behind positions. That would be a major step.
• Posted by a hidden member.
TigerTim said
Christian73 saidTim - You realize, of course, that Socal isn't really interested in logic. If so, he couldn't post the kind of nonsensical sources he does on a regular basis.

Well I think he wants to think he is. Which is sort of laudible, no?

Perhaps you might take a look at Christian's posts in the link referenced in the OP.
• Posted by a hidden member.
socalfitness said
TigerTim said
Christian73 saidTim - You realize, of course, that Socal isn't really interested in logic. If so, he couldn't post the kind of nonsensical sources he does on a regular basis.

Well I think he wants to think he is. Which is sort of laudible, no?

Perhaps you might take a look at Christian's posts in the link referenced in the OP.

Well it was interesting from an animal behavior perspective but not much else.
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