How do you master logic?

[logicaalroy]

The field of legal reasoning applies its own approaches to special topics that are in the intersection of law of logic. I have not opined that logic in its many forms and applications does not reduce to inductive logic or deductive logic. However, certain fields of study may concern themselves with the application of logic in the context of certain considerations especially important in those fields. . . But the field of legal reasoning does exist and has special things to say about certain kinds of arguments. If this does not interest you, then that's fine with me; though I don't see how I can be faulted for simply reminding someone who expresses an interest in logic especially applied to argumentation that there is a field for logic especially applied to legal argumentation. . . .

My poster name is 'LauricAcid' not 'Laura'.

Hi LauricAcid,

I am sorry to write your name incorrectly. My Fault. However, if as you say "logic in it's many forms and applications . . . [DOES] reduce to inductive or deductive logic" then leagal reasoning will follow those same rules of inference. For example there are 21 rules of inference in deductive logic. Does legal reasoning use other rules of inference? If they use the same rules of inference and avoid fallacies, I don't see the point in making a distinction of legal reasoning. I can understand if you really mean to say that in the legal field the answers aren't logically derived then that is what you should have stated. Many people realize the judges make their own decisions based on the evidence in the case, but some are biased to start. For example, we know that John Roberts is against abortion and if he becomes Chief justice he is likely to try to over turn Roe vs Wade [especially because Bush has another nomination who will most likely also be against abortion]. Way to dictate Bush! This is not legal reasoning. Its use of authority. Where people have authority are places people can abuse it.

[LauricAcid]

I have too little at stake in the matter to motivate me to dissuade you from whatever your view is of legal reasoning. If you claimed that the field of legal reasoning is a banana split with walnut syrup topping, I'd just as soon let you keep thinking that.

But I am intrigued by your mention that there are twenty-one rules of deductive inference. What do you think are these twenty-one rules?

[logicaalroy]

I have too little at stake in the matter to motivate me to dissuade you from whatever your view is of legal reasoning. If you claimed that the field of legal reasoning is a banana split with walnut syrup topping, I'd just as soon let you keep thinking that.

But I am intrigued by your mention that there are twenty-one rules of deductive inference. What do you think are these twenty-one rules?

Hi LauricAcid,

I did not reply to your use of the term "legal reasoning" to have you dissuade me. I like many others doubt the legitimate use of the term and suggest to you your terminology is off . Your use of the term "legal reasoning sounds as if there is a distinct form of reasoning when you can't distinguish that from deductive. Your choice of words simply confound people and would confuse anyone new to logic. A better choice of word would be easier: "reasoning as done in the legal system includes things other than deductive logic."

As to the 21 rules of inference I mentioned, they are as follows (according to the logician Irving M Copi):

Modus Ponens

Modus Tollens

Disjunctive Syllogism

Hypothetical Syllogism

Constructive Dilemma

Destructive Dilemma

Simplification

Conjunction

Addition

Absorption

DeMorgan's Theorm

Double Negation

Commutation

Association

Distribution

Transportation

Material Implication

Exportation

Material Equivalence

Tautology

Reductio Ad Absurdum

Conditional Proof

NOTE: Many people put Reductio Ad Absurdum into the Conditional proof category and thus 21 rules of inference is stated. Any of these can be looked up for their logical notation (it would be a monsterous task for me right now). If you do want to see any logical notation on a specific one I can oblige.

but what rules including Predicate logic? Do those count? I didn't even count those.

[LauricAcid]

Thanks for you answer, logicalroy.

You're on the right track by asking about predicate logic. Indeed, there are many more deductive systems other than sentential logic.

Also, that list of 21 rules is just Copi's own list for his own presentation of sentential logic. Sentential logic can be formulated in many different ways with different rules and axioms. In fact, rather than use those 21 rules we could reduce sentential logic to just one rule with one axiom and using just one binary connective.

[PioDJM3000]

I am an undergrad student interested in logic. I really don't care much about philosophy, but I am absolutely fascinated with logic. But this in neither here nor there.

What I would like to know is how do you perfect your logic? Is there some sort of exercise book, or text book?

Here are a couple of great old books that have been reprinted and come highly reccomended from Objectivist scholars.

1. Lionel Ruby. Logic: An Introduction.

2. H.W.B. Joseph. An Introduction to Logic

Though they both say they are "intros" they are both very advanced in comparision to what is coming out today. Especially the one by H.W.B. Joseph.

These books can be purchased at http://www.papertig.com/