Dear Yaoszh.

I hope that what follows, which is based on Wikipedia, is of some help for you concerning what logic is.

Logic is the systematic study of the form of valid inference and the most general laws of truth. A valid inference is one where there is a specific relation of logical support between the assumptions of the inference and its conclusion. In ordinary discourse, inferences may be signified by words such as therefore, hence, ergo, and so on.

There is no universal agreement as to the exact scope and subject matter of logic but it has traditionally included the classification of arguments, the systematic exposition of the 'logical form' common to all valid arguments, the study of proof and inference, including paradoxes and fallacies, and the study of syntax and semantics. Historically, logic has been studied in philosophy (since ancient times) and mathematics (since the mid-19th century), and recently logic has been studied in computer science, linguistics, psychology, and other fields.

The concept of logical form is central to logic. The validity of an argument is determined by its logical form, not by its content. Traditional Aristotelian syllogistic logic and modern symbolic logic are examples of formal logic.

Informal logic is the study of natural language arguments. The study of fallacies is an important branch of informal logic. Since much informal argument is not strictly speaking deductive, on some conceptions of logic, informal logic is not logic at all.

Formal logic is the study of inference with purely formal content. An inference possesses a purely formal content if it can be expressed as a particular application of a wholly abstract rule, that is, a rule that is not about any particular thing or property. The works of Aristotle contain the earliest known formal study of logic. Modern formal logic follows and expands on Aristotle In many definitions of logic, logical inference and inference with purely formal content are the same. This does not render the notion of informal logic vacuous, because no formal logic captures all of the nuances of natural language.

Symbolic logic is the study of symbolic abstractions that capture the formal features of logical inference. Symbolic logic is often divided into two main branches: propositional logic and predicate logic.

Mathematical logic is an extension of symbolic logic into other areas, in particular to the study of model theory, proof theory, set theory, and recursion theory.

However, agreement on what logic is has remained elusive, and although the field of universal logic has studied the common structure of logics, in 2007 Mossakowski et al. commented that it is embarrassing that there is no widely acceptable formal definition of 'a logic.

Logical systems

A formal system is an organization of terms used for the analysis of deduction. It consists of an alphabet, a language over the alphabet to construct sentences, and a rule for deriving sentences. Among the important properties that logical systems can have are:

Consistency, which means that no theorem of the system contradicts another.

Validity, which means that the system's rules of proof never allow a false inference from true premises.

Completeness, which means that if a formula is true, it can be proven, i.e. is a theorem of the system.

Soundness, meaning that if any formula is a theorem of the system, it is true. This is the converse of completeness. (Note that in a distinct philosophical use of the term, an argument is sound when it is both valid and its premises are true)

Expressivity, meaning what concepts can be expressed in the system.

Some logical systems do not have all four properties. As an example, Kurt Gödel's incompleteness theorems show that sufficiently complex formal systems of arithmetic cannot be consistent and complete;[however, first-order predicate logics not extended by specific axioms to be arithmetic formal systems with equality can be complete and consistent.

Kind rgeards,

Orlando

Very learned scholar, Orlando.

To do what it is reasonable

To explore our mind

Dear Yaozhi Jiang

Why do we need the environment? Why do we need our Memories? Why do we need water? Why do we ask questions such as this one you asked? BIG CLUE: modern thinking IS outrageously and unjustifiably DUALISTIC: There is this and there is THAT, so why not allow ourselves to ask about either (this or that)?(and then, basically, "ask" about anything, no matter how far off the so-called "level of analysis" is). (I believe my response may be one of the better overall responses to your question, though some philosophers may be able to conjure "more".)

You also make some statements that are incorrect or gross over-statements:

You say: " Subjective world only has subjective information. " Try to explain and justify THAT. Much of what we should know to be more rational ourselves may be subjective knowledge of some people RIGHT NOW.

You said: " ... objective logic? Obviously is cause-effect law that produces all events or things or matters in objective world " Really? And, that's it? (How about simply knowledge of important properties of things, and why they are important? -- often in ways not seen as cause-and-effect, in any clear or reasonable sense. Here is an example: Food is often good tasting, so ("therefore", if you like) we are inclined to eat it.)

If you want to say something wild, like " Human beings holds the objective logic via subjective logic only. ": Why not try RATHER: we come to know actual (ultimate) Realities only by way of our conventional realities. A good correction, I think, for you to make. Plus, "ditch" the dualism(s) -- it fails.

"logic is the morality of thouhght such as morality is the logic of action"

Jean Piaget

From a common language perspective, logic in sound thinking

Dear Brad Jesness:

Thanks for your good comments.

Any person, when he/she was born, his/her brain was bare and unrationality, follow his/her growth process his/her impressions from objective world has been built up, this process we call as cognization to objective world. This cognizablity of human beings is intelligence. Just the cognizablity of human beings make the world is divided into the two worlds, objective world and subjective world. Maybe "dualism" as you said.

Why do we need to eat? because of food means energy and matieral to human beings, although this is not only a problem about evolving theory, but also a problem in philosophy.

Why do we need to live? because of we are all negative entropy collectors in world, God rules us all. We have to do something difficult to understand as we do every day forced by lusts. Fatalism perhaps is the best answer!

Evolving process is magic and not easy to understand, we do not as our pleases, this is natural ruler that we have to accept.

Thanks for your attention, I do be care of "ditch" the dualism.

Thank you again!

The study of reasoning and fallacies.

Logic is a good tool to detect mistakes in our reasoning. A word without logic would be incoherent and senseless.

Orlando Lourenço.

Dear Orlando M Lourenço

And because of what you last said, which indeed is true: Should we be asking "why we have something" that, if we did not have it, we would be extinct? It might make sense in the sense of "why" for discovering its development, no doubt parts at a time (as Yaozhi Jiang says: it develops -- though (I believe) it is never, in notable significant ways, ever absent). ALSO notice we all are automatically "translating" Yaozhi Jiang's Question because:

"Logic" is just a FORM (kind of like: rectangle). If you have invalid premises, it yields garbage; certain things can well be rectangular, others not. We all automatically know "logic" is not what he meant.

Overall conclusion: The actual Question, therefore, which Yaozhi Jiang tried to ask, would have to be translated into "why do we have sound thought?" (which is really the Question I and several have been responding to all along) . But, even with that translation, it is true that, if we did not have it, we would be extinct and thus asking "why", as if we could figure that KIND of thing out as some kind of distinct whole concept, all-at-once, and IN GENERAL, is (again, as so many similar instances) an un-true way to think about things, basically by "biting off more than one can chew" (that is to say: trying to/pretending-to (irrationally) "stuff" more in working memory than will fit) -- which is the fundamental error of philosophy (making most of it worthless or worse); this practice necessitates and leads to incorrect, serious over-generalization.

"Sound thinking" is also just a type of thing ( a "form") -- one cannot investigate "types" of behavior patterns UNLESS they are distinctly true and real types * (basically: biologically)(our actual Memories need that sort-of/degree-of "help") and, even then, the answer is not going to come in one "fell swoop". Everyone must move to love true empiricism more (with an "eye to" some key directly observable, overt phenomenon always) -- otherwise, at best, people do not know what you are talking about (and maybe you don't). Agree?

* FOOTNOTE: This is something Psychology, it seems, cannot learn; on fundamentally NO legitimate bases, they have models (conjured up hypothetico-deductive systems -- with "conjured" being very much the correct word). Perhaps it is best to view Psychology as one of philosophy's worst examples (or worst systems) (rather than pretend philosophy is not involved) -- its "concepts" have been "hammered on" and, at times, slightly shifted over and over and over, with basically no improvement (almost always bad, much like philosophy; similarly a product of "the minde" -- armchair "drifting" 'thought'). I have dedicated my life of 65 years (or at least 50 years) to Psychology, yet see most of it as, at least largely, of either little good (relative to what may become the real thing _and_ become of that) or of no good. Basically, the same in nature for its 100 yr+ history. (My favorite areas, the Memories and Development, are only slightly researched and wrongly concluded about; there is a "kernel" of good "hidden" in each of these areas, though -- i.e. even some likely good findings, which I have been able to locate.)

Deat all,

Paraphrasing Wittgensten, I would say that logic is a conceptual tool that helps us avoid that our thinking is bewitched by our language.

KInd regards,

Orlando

As I see it, logic is the prime virtue of cognitive systems, such as justice is the prime virtue of social systems.

Kind regards,

Orlando

Prime virtue is very important, a problem of ethics.

I must sadly say that "logic" is only a term of victory.

Deductive logic refers to conclusions where all the premises are true, and in which case, there can be no way for the conclusions to be false. The fundamental element in deductive reasoning is syllogism, where a deduction is inferred from two suppositions, each of which has one term in common with the conclusio

Logic: is the science that teaches the rules and laws of the general human reflection: By learning the rules of logic we can criticize the ideas and theories of science, and we will identify the types of errors and identify the causes and thus it develops the spirit of cash in his school.

Dear logic community,

As I see it, we need logic very much. It is through logic that we can see the coherence of an argument or even a theory. Logic, however, is not a unitary concept, because logic can be based, for example, on induction, deduction and abduction. There is also the propositional logic and the modals logic. For the sake of brevity, I do not elaborate on these types of logical. I also assume that these types of logic are known by those who participate in this thread.

Best regards,

Orlando

Logic is a science about thinking and reasoning.

Is the study how to evaluate the arguments.

Logic is, say, the morality of thought such as morality is the logic of action

Dear Yaozhi Jiang

Logic is a "form". It is a good form, and necessary, but has no substance unto itself [(that is why there is the additional word, "sound")]. [ I have known/realized this for many decades and seen no evidence otherwise -- and there is NONE even officially because, as I say it is, is as it is represented by philosophers themselves. ] Anyone who thinks/says there is more to it is incorrect and likely not a good or independent thinker.

Dear Orlando M Lourenço

It seems to me that a kind of good analogy is: morality is to ethics AS logic is to soundness (but this certainly is NOT a perfect analogy).

Dear Jiang,

Logic is a tool. The introductory part in the natural process of the mind. Being able to accept things naturally. Underlying an action that leads to the truth. As a comparison of a person's thinking conditions towards something that is being faced. Objective input in assessing something.

Regards.

I Putu.

Thanks for I Putu-Artaya's comments.