View Poll Results: Is the argument logically valid?

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  • No, the argument is not logically valid.

    3 37.50%
  • Yes, the argument is logically valid.

    5 62.50%
  • I don't know.

    0 0%
  • The question doesn't make sense.

    1 12.50%
  • The argument doesn't make sense.

    0 0%
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Thread: Everyone is female... Therefore ... ?

  1. Top | #31
    Contributor Speakpigeon's Avatar
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    OK, so here we have a clear majority of voters who think the argument is valid. Those who think the argument is not valid haven't properly explained why.

    One crucial point about this argument is that it is not formally valid.

    That the argument is not formally valid can be seen by the fact that its validity doesn't depend only on the explicit form of the argument.

    Everyone is female;
    Therefore, any siblings are sisters.
    Specifically, to understand the argument as valid, you need to assume what the three non-logical terms mean: "female", "sibling, "sister".

    Bomb#20 has been kind enough to provide a convincing interpretation of these terms whereby the argument is not valid.

    Please note that professional logicians, however incompetent I think they are, nonetheless usually accept that this argument is valid even though they would all say that it is not formally valid. The distinction is indeed often part of the way logical validity is explained in textbooks.

    This shows that, contrary to what fast argued, the notion of validity simpliciter, as opposed to formal validity, is accepted by professional logicians as our ordinary, layman notion of the logical validity of an argument, as it is demonstrated here by the answers of most posters.

    Thus fast wrongly argued that validity is a technical term in the context of logic when in fact the proper technical term is "formal validity".

    Of course, mathematicians themselves will usually use the term "validity" rather than the technical term "formal validity" when they in fact mean formal validity, thus confusing fast as to which is the technical term.

    So, will fast now blame mathematicians for using the non-technical term "validity" in lieu of the technical term "formal validity", thereby confusing his judgement?

    The argument above could be made formally valid by making explicit our implicit assumptions about what the non-logical vocabulary means:

    p1 - For all x, Sister(x) implies Female(x);
    p2 - For all y, Sibling(y) implies either Sister(y) or Brother(y);
    p3 - For all z, Female(z);
    C - Therefore, for any a, Sibling(a) implies Sister(a).
    It is noteworthy that most people would find it more difficult to assess the validity of the formalised argument, essentially because it is more complicated and wordy, and this even though this is essentially the same argument. This falsifies the idiotic claim that people are confused about validity. People will undoubtedly be confused about formal arguments given that most people don't have the proper training to read them, but they are not confused about validity, as demonstrated by the answers given here.
    EB

  2. Top | #32
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    Quote Originally Posted by Speakpigeon View Post
    This shows that, contrary to what fast argued, the notion of validity simpliciter, as opposed to formal validity, is accepted by professional logicians as our ordinary, layman notion of the logical validity of an argument, as it is demonstrated here by the answers of most posters.

    Thus fast wrongly argued that validity is a technical term in the context of logic when in fact the proper technical term is "formal validity".

    Of course, mathematicians themselves will usually use the term "validity" rather than the technical term "formal validity" when they in fact mean formal validity, thus confusing fast as to which is the technical term.

    So, will fast now blame mathematicians for using the non-technical term "validity" in lieu of the technical term "formal validity", thereby confusing his judgement?
    You’re confusing “formally valid” with “logically valid.” You think that if the formality of a logical argument is redacted, then the discussion has changed. It has not. I’ll give you credit for making a go at it though. You really do put in effort.

    To illustrate through storytelling (fast style), let every reader understand and remember that it’s always about the rain. Anyone having a discussion about validity just needs to see if their clothes are wet in order to discern which variety of validity is actually under discussion. There’s out of classroom validity (where rain never lets up), and there’s in the classroom validity (where all remain bone dry). Oh, and it’s always raining, and if but only a brief moment, you discuss out of classroom validity, you will get drenched, quick-like.

    If a group of otherwise intelligent people are discussing whether or not an argument is valid, you may happenchance notice collective agreement among them, but don’t for a minute mistake their collective agreement or disagreement with whether or not they understand logical validity IF they are soaked head to toe. Logical validity is an in the classroom discussion. When you see the rain-a-pourin’, you see agreement on an outside topic—not an inside topic.

    Outside the classroom settings almost always include a use of “valid” that is untamed and have no qualms venturing out in the misty outdoors where rain falls from canopy’s in the jungle of normal lexicon. That’s why I say consult a dictionary if you want to understand what that unsophisticated version of logic means.

    But, when you walk through the hallowed walls and sit before the professor, he’ll ask each of you in turn what YOU think validity is. A playground full of short snippet ideas will domino around the room—like a great body wave circling a football stadium. Each will have had an opportunity to spill out their two cent change—AND THEN they’ll begin to dry as the class ruler hammers in the minds of the commoners exactly how it will be used in between the dry walls where people go to learn how it’s used IN logic.

    The INSIDE notion of validity is just what it is, whether formalized or not. What “validity” means does not change when an argument is formally written. If anyone thinks otherwise, check your clothes. Validity, formalized or not, remains a topic of logical validity. The only way the discussion goes from logical validity to common everyday validity is if you go outside—and if you do, I suggest carry an umbrella.

  3. Top | #33
    Contributor Speakpigeon's Avatar
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    If you can't explain yourself in one sentence you'll be left out to dry.

    This is my thread. Where is the teacher you are talking about?! There's no teacher here to impose any technical notion. Just us. So your contention that just because I asked about logical validity therefore it's a technical sense doesn't make sense.

    Remember what the question is: Do you personally think this argument is logically valid?

    I didn't ask whether you think the teach think the argument is valid.

    Validity is validity as Aristotle defined it and he defined validity on the basis of his observation of the way philosophers and politicians at the time argued and talked.

    And this is why the mathematical logic definition is wrong and why even untrained people are correct.
    EB

  4. Top | #34
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    Quote Originally Posted by Speakpigeon View Post
    If you can't explain yourself in one sentence you'll be left out to dry.

    This is my thread. Where is the teacher you are talking about?! There's no teacher here to impose any technical notion. Just us. So your contention that just because I asked about logical validity therefore it's a technical sense doesn't make sense.

    Remember what the question is: Do you personally think this argument is logically valid?

    I didn't ask whether you think the teach think the argument is valid.

    Validity is validity as Aristotle defined it and he defined validity on the basis of his observation of the way philosophers and politicians at the time argued and talked.

    And this is why the mathematical logic definition is wrong and why even untrained people are correct.
    EB
    You persist on qualifying the word “valid” with the word “logical.” If you want us to answer the question you have in mind, you might try refraining from doing that.

    What you’re doing is not unlike what Untermenshe used to do with the term “logical possibility,” yet everyone knows that we do not use a dictionary (but rather a glossary) to determine what that two-worded term means. In other words, we do not look up the individual words and walk away with an accurate understanding of the term’s meaning.

  5. Top | #35
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    Quote Originally Posted by Speakpigeon View Post
    Quote Originally Posted by ronburgundy View Post

    It is not deductively valid. It becomes valid only if one adds the premise "Female siblings are always sisters."

    While this premise may seem so obviously true by definition that we normally would not verbalize it, deductive validity is determined only upon explicitly stated information.
    Ok, but what do you think people mean here when they say it is valid? Do you think they mean "not deductively valid"?

    You seem to understand the reasoning behind the assessment that the arguent is valid. Isn't it enough to make the distinction between valid simpliciter and formally valid? It seems to me that you are talking about formal validity, whereby we require all premises to be made explicit...
    EB
    I think people who say it's "valid" are using the term loosely, but that by the standard notion of logically validity an argument is required to explicitly state all premises that make the conclusion neccessary. A logically valid argument is one where all the concepts can be replaced with abstract tokens and it still is equally sound, meaning that no particular prior knowledge of the meaning of each concept is required to know that the argument is valid.

    If the listener must insert their own previously presumed knowledge or beliefs into the argument to make the conclusion warranted, then the "validity" is not a property of the argument itself but only a product of the listeners beliefs combined with what is in the argument.

  6. Top | #36
    Contributor Speakpigeon's Avatar
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    Quote Originally Posted by fast View Post
    Quote Originally Posted by Speakpigeon View Post
    If you can't explain yourself in one sentence you'll be left out to dry.

    This is my thread. Where is the teacher you are talking about?! There's no teacher here to impose any technical notion. Just us. So your contention that just because I asked about logical validity therefore it's a technical sense doesn't make sense.

    Remember what the question is: Do you personally think this argument is logically valid?

    I didn't ask whether you think the teach think the argument is valid.

    Validity is validity as Aristotle defined it and he defined validity on the basis of his observation of the way philosophers and politicians at the time argued and talked.

    And this is why the mathematical logic definition is wrong and why even untrained people are correct.
    EB
    You persist on qualifying the word “valid” with the word “logical.” If you want us to answer the question you have in mind, you might try refraining from doing that.

    What you’re doing is not unlike what Untermenshe used to do with the term “logical possibility,” yet everyone knows that we do not use a dictionary (but rather a glossary) to determine what that two-worded term means. In other words, we do not look up the individual words and walk away with an accurate understanding of the term’s meaning.
    You are the only one to have a problem here.

    We don't need a dictionary. We all understand the two words, "logical", and "validity", and therefore we all understand the expression "logical validity".

    The argument is a logical argument and, like it or not, the validity we are talking about here is logical validity, not any other kind of validity.

    If you think this is misleading, you haven't demonstrated that it is. To do so, you would need to show that logical validity is somehow from the validity of a logical argument. I don't n=know of any reason to accept that.

    I took the argument in question from the book I have on logic written by a Peter Smith:

    Peter Smith retired as lecturer in the Faculty of Philosophy at the University of Cambridge. Previously he taught at Aberystwyth and Sheffield, and for twelve years he was editor of the journal Analysis. He has written books in the past on the philosophy of mind and on chaos theory; now he mostly works on logic-related matters, and his last book was on Gödel's theorems.
    He himself used the argument in his book as an example of a valid argument, to explain the difference between validity simpliciter and formal validity.

    And definitely not between validity and logical validity. It's all in your mind and it is clear you're not any kind of expert on logic.

    As to UM, no it's not the same situation at all. UM insisted possibility was physical possibility, whatever that could possibly mean given that talk of a physical possibility is incoherent outside what is actual, making the notion trivial. Me, I am talking of logical validity because we're discussing the validity of a logical argument. And again, you're the only one to see a problem in that and you are unable to explain what it is.
    EB

  7. Top | #37
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    Quote Originally Posted by Speakpigeon View Post
    The argument is a logical argument and, like it or not, the validity we are talking about here is logical validity, not any other kind of validity.

    If you think this is misleading, you haven't demonstrated that it is. To do so, you would need to show that logical validity is somehow from the validity of a logical argument. I don't n=know of any reason to accept that.
    A correction may be required here:

    If you think this is misleading, you haven't demonstrated that it is. To do so, you would need to show that logical validity is somehow different from the validity of a logical argument. I don't n=know of any reason to accept that.
    EB

  8. Top | #38
    Contributor Speakpigeon's Avatar
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    Quote Originally Posted by Speakpigeon View Post
    The argument above could be made formally valid by making explicit our implicit assumptions about what the non-logical vocabulary means:

    p1 - For all x, Sister(x) implies Female(x);
    p2 - For all y, Sibling(y) implies either Sister(y) or Brother(y);
    p3 - For all z, Female(z);
    C - Therefore, for any a, Sibling(a) implies Sister(a).
    LOL, my formalisation is NOT valid!

    Nobody noticed or what? With all the "experts" here on mathematical logic and Boolean algebra? That is quite surprising!

    Quote Originally Posted by Speakpigeon View Post
    It is noteworthy that most people would find it more difficult to assess the validity of the formalised argument
    Seems like a QED to me.

    Please note it wasn't intended. I thought myself my formalisation correct and valid, but no.

    So here is a valid formalisation. Only the first premise needs to be replaced:

    p1 - For all x, Brother(x) implies not Female(x);
    p2 - For all y, Sibling(y) implies either Sister(y) or Brother(y);
    p3 - For all z, Female(z);
    C - Therefore, for any a, Sibling(a) implies Sister(a).
    Are we sure it is valid now?
    EB

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