If a conclusion is logically valid, is it necessarily true? Why or why not?

Question

If a conclusion is logically valid, is it necessarily true? Why or why not?

Answer 1

Roger is wrong when he states: "the process of logic may be good but the premises false."

If the premises are false, the logic is "invalid," not valid. http://www.iep.utm.edu/v/val-snd.htm

That link also demonstrates when a "valid" conclusion is also true or not. It does not have to be true, if it is not "sound."

"Facts not in evidence" have no bearing on the issue of validity. Just as long as the premises are assumed to be factual, it makes for a valid syllogism.

Many syllogisms are valid which have utterly preposterous premises. But the test of validity is ONLY to determine whether or not the process has followed the rules of logic.

Then and ONLY then can you determine the "truth" (soundness) of the conclusion.

Answer 2

No it may not be true and I would also say that what is not logically valid might be true as well. Suppose you logically prove the nonexistence of god does that mean god doesn't exist? Do you expect other to take your statement as true? And if I fail to prove the omnipotence of god logically does that mean I'm wrong?

Answer 3

First an answer to the question. No. The Socrates example up there (Roger) makes this point. It's valid but it's not a necessary truth. There is no logical contradiction in thinking that a man be immortal.

That aside, there is some serious misinformation in a lot of the answers here. I don’t think this helps answer the question but we need some clarification. I’ll work my way down.

Roger is right. Everything he says is fine. I take him to be talking about validity when he is talking about the ‘process of logic’.

Yaoi, who is usually good at this stuff, is wrong. I would suggest following the link provided to check but the truth or falsity of the premises has absolutely nothing to do with the validity of an argument. An argument with all false premises can still be valid it just can’t be sound. To be honest, I think Yaoi gets this near the end of his post but that first part is simply false.

Zoe is also right. An argument’s validity can be determined by looking at the truth tables associated with it. If there is a row in which all the premises are true and the conclusion false then the argument is invalid.

Nick is right but has jumped from talking about propositional logic to syllogistic logic which has a different set of rules. The claims about undistributed middle and soundness are fine on their own but he calls Zoe out when she’s right in that she’s talking about propositional logic.

Sorry this was extended I just wanted to clear the water.

Answer 4

No, because the process of logic may be good but the premises false.

All men are mortal.

Socrates is a man.

Therefore Socrates is mortal.

Valid and true.

All fruit is poisonous.

Tomatoes are a fruit.

Therefore tomatoes are poisonous.

Valid but false.

Answer 5

True for now. Til new info is found.

Answer 6

i think that "Yaoi" is wrong and Roger is right. the argument can only be invalid when all the premises are true and the conclusion is false. if at least one of the premises are false, or the conclusion is false then the argument is rendered valid by default.

in answer to the actual question, roger explains it well.  

Answer 7

No, a logically valid conclusion is not necessarily true due to unknown factors. We can draw a valid conclusion using logic and the facts in evidence. The problem lies in the facts NOT in evidence. i.e. data we don't have.

Answer 8

A couple of people on here are incorrect and need to rediscover their logic text book. For instance, Zoe B says that an argument can only be invalid if all the premises are are true and the conclusion false. This is false, actually. Validity, in logic, is that which has to do with the form of the argument not the truth of the premises. An example of an argument with all true premises, including the conclusion but which is invalid is:

The INTERNET conveys information

Whatever is informative conveys information

Therefore, the Internet is informative

The problem here is that the middle term is undistributed resulting in the fallacy of "Undistributed Middle". It only tells us that the INTERNET is of the category "things that convey information". But, there are other things in that category as well, like professors and news papers.  This, of course, renders the argument invalid, since formal fallacies have to do with the form of the argument and therefore the validity of it. However, I hardly think any one would argue with the propositions of the argument. So, while there can be all true propositions making up and argument the argument can still be formally invalid.

Further, nobody (at least I didn't see any one mention it) mentioned a common mistake made by beginners. Arguments ARE NOT true! The premises of the argument, being declarative statements, are either true or false. The form of the argument (discussed above in brief) has to do with validity. "Soundness" is the quality of an argument that shows it to be proved (not true). When the premises of an argument are true, and the form of it is valid, then we say that necessarily that the argument is "sound". An argument can have all true premises and be invalid. It can also have false premises and be valid; but, the sound argument, that is to say the good argument, is that which has both valid form and true premises. So, even though an argument may be valid it isn't necessarily "sound" (not true as you have in your question) since it can have false premises.

A good book, although Christian in origin, is Socratic Logic. Now, simply because a person is a Christian does not render his ability to do logic more dubious than one who is non-theistic. Although, most of the Atheists on here are going to say otherwise. Again, this book is very easy to read and the author has a keen ability to explain the terms and methods well. Look in to it if you are serious about enhancing your logical abilities.

Good luck.

Answer 9

good and valid are not interchangeable terms.

Valid arguments need not be true

Mr Yaoi is correct regarding syllogisms, Rogers examples are examples of justification of validity. Both gentlemen answer the question properly.

Answer 10

If it will get you elected, make you money or get you laid then yes.

If not then who cares?

Answer 11

hey roger there is a difference between valid and logic ...logic is valid but valid