A Logical Problem
Ok, I’m taking a class in symbolic logic this semester. It’s been an interesting class thus far, I’ve found out several interesting life truths, namely that if you throw out a little Latin in the first couple sessions, you get called on for answers a lot more. I’ve also learned that my natural inclination towards post modern ideals can be a deterrent when dealing with a two valued system (everything is either true or false, for the purposes of our learning of systematic logic).
So, I will happily acknowledge that I am not the smartest person in my class. I similarly acknowledge the intelligence of my professor, as evidenced by his doctorate in Logic. I know that he did work for the pentagon as a cryptologist (and has told us every night he dealt with 9 valued truth systems). I know he teaches this course at Georgia Tech to masters degree students. I get it, he’s smart(er than I am).
Ok, now that the set up is complete– I disagree with the man. I don’t think he’s a great teacher to begin with. He spent thirty minutes talking to us about Aristotelian logic before saying that “you can disregard all of that, as we wont be using it for the purposes of this course”, the he proceeded to yell at us for leaving after the class period was up, since he was not done with his lecture. I know I’m a lowly undergrad, but respect my time and I’ll respect yours- don’t go off on a tangent and then hold us late to make up for it. He also has issues adapting to the needs of his students, a student told him that he was a visual learner, and if the professor could work out the problems on a white board. The professor gave that poor student a disgusted look and proceeded to tell him we were doing this course “discursively”, but if we needed to expend time working out issues on the board he would acquiesce.
Ok, now that I’ve built him up and torn him down, here is my problem, and those of you that have dealt with logical systems can perhaps clarify the issue for me.
We were given this (basic) problem, simply as an example of a “valid” argument.
All horses are green. All green things are immortal. All horses are immortal.
Ok, yes, while not a sound argument, it is indeed valid. A fellow student, however, asked the professor “If we change the conclusion to state ’some’ instead of ‘all’, would the argument still be valid?” My professor told the student that the argument would no longer be valid. Which threw me off.
While the argument may no longer be precise, or perhaps no longer be ‘as valid’ as it was when it read “all”, the argument still appears to me as valid. If some is indeed a subset of all, then the conclusion has not gone outside the properties given within the premises, and thus would retain it’s validity.
Am I right here?
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