Just recently saw the following argument in a logic book: all lions are herbivores all zebras are lions ————– therefore all zebras are herbivores this seems to be logically valid syllogism, but it is disturbing.

I have been reading your site, and there is somewhere you said a conclusion can logical valid but unsound. Is the following argument valid but unsound? I am not sure about what unsound arguments mean? Can you please clarify this for me. – Johnson Mafoko

Yes, that is a valid, unsound argument. The structure is good, but the content is bad. This is the case even though the conclusion is correct.

The way it works is this:

Invalid means the structure is bad. There are no benefits to an invalid argument, the premises have no meaningful connection to the conclusion.

Valid means the structure is good. If an argument is valid, it means the conclusion is at least as good as the premises. So if you put in true premises, you get a true conclusion. However, it doesn’t mean that if you put in false premises you get a false conclusion. In logic, false premises can lead to any conclusion, even when the argument structure is valid.

Sound means that the argument is valid and that the premises are true. A sound argument will guarantee a true conclusion. It is the only type of argument that guarantees a true conclusion.

Please note that only “formal” arguments –the kind of very artificial, highly structured arguments found in logic books and dealing only with unambiguously true or false statements –can be either valid or sound. (Different terms are used for less formal arguments).

Related content:

  1. A circular argument is technically a valid argument. For every case in which the premises are true, the conclusion will be true. So what makes it a bad one?
  2. 1) The claim “There is extraterrestrial life in the universe, because my father said so” is an example of an appeal to authority. But it can be viewed as an enthymeme, where the hidden assumption is that “my father is always right”. In such a case, there is no logical problem with the argument. Do you agree? 2) Do you think that to say that : “Person A is biased , therefore\what he says is wrong” is fallacious? It can be interpreted as “person A is biased, therefore his information cannot be trusted. Therefore what he says is wrong”. 3) Are errors of logic errors of psychology as well? Or perhaps, only errors of psychology? Appeal to authority besides being a logical fallacy, has a whole psychology and sociology besides it.
  3. Inductive arguments establish objective facts, so how can they be considered subjective?
  4. I would take a standard textbook on math, where all the propositions are correct. Write down 99 correct mathematical statements. And then add “Zeus exists”, and compile a text. Then I would argue, that if we have a box, from which we sample randomly 99 balls and they are have the property of being black, we can think with good reason that the next one will be black. And therefore, since 99 of the math propositions in the texts are have the property of being correct, there is good reason to think that “Zeus exists” is also correct. It seems wrong somewhere. But where?
  5. On one hand, arguments are supposed to be objective – something which is true is always true, for everyone. On the other hand, if person says “P exists because X,Y,Z”, while he personally has seen the evidence (x,y,z) for P, and another person says “P exists because X,Y,Z” and he has only read about X,Y,Z from second sources – their knowledge is actually very different. Where is that difference (crucial one) reflected in logic?
Better Related Posts Plugin

Leave a Reply

Your email address will not be published. Required fields are marked *