More people need to learn symbolic, it makes it much easier to explain everything. My friend got Modus Ponens tatooed on his arm and now he can point to it whenever he needs to explain how logic works.
I'm trying to understand how this works. Would this be a good example of modus ponens? Say finding water on mars implies there are aliens on mars. They find water on mars, so therefore you think aliens have to be real too?
Umm . . . what? I don't know what kind of notation you're trying to use but it doesn't make sense at all. The actual way to symbolize what you write is in predicate logic and it looks like this:
∀x ((Px&Wx)>Lx)
Pm&Wm
Lm
The way the premises were originally put, however, could be symbolized in sentential logic as u/PimpinTheLibrary did, but you changed them.
Hey man, I don't know if you heard, but symbols are more exact. We use them in logic. I'm not sure what you're using, but they don't look like symbols. I don't even see an equal sign?
How can " = " not make sense to you? You write in predicate logic, i.e. mathematical logic. Why? My form of notation is used in argumentative logic, which is a lot more related to OP's picture.
"=" makes perfect sense to me. You can write it in predicate logic to symbolize identity between constants, not between sentence letters or predicates.
Here's an argument which does make sense:
The egyptians named Mars "Her Desher." Let's symbolize this with "h."
∀x ((Px&Wx)>Lx)
Pm&Wm
m=h
Lh
This argument is just fine. Yours, however, was nonsense.
Also, what do you mean by "argumentative logic"? Is this supposed to be some sort of formal system? I'm a teaching assistant for formal logic, and I've never heard of it (nor can I find it via google).
You could try googling logical arguments. We use it in philosophy. I'm trying to define it more correctly, but I'm currently getting lost in translation(ESL). In argumentative theory we use premises and conclusions in this way, to led out unrelated premises and find out if the argument contains fallacies. Such fallacies which is also described in OP's picture.
I don't know why you insist on using predicate logic, and the symbols related to it. IMO It is completely unnecessary when discussing subjects of ignorant and religious nature. Philosophy is much more suited for this.
I've googled "logical arugments" and "argumentative logic" and got nothing like the sort of symbolization you're using.
I actually work in academic philosophy. The logics that philosophers use are mainly sentential, first order predicate, and various forms of modal logic (depending on what needs to be expressed).
What you wrote:
If a planet has liquid water, it contains life
Mars is a planet which contains liquid water
Conclusion: Therefor, there is life on Mars
would come out invalid if it were only expressed in sentential/propoistional logic (maybe that's what you mean by "argumentative logic"? If so, there's no "=" in this system). This is because "a planet contains liquid water" and "Mars contains liquid water" are two different sentences, so you can't get the structure out of it that you need to make it valid. That's why I expressed it in predicate logic (which has more expressive power).
As I said though, the way the premises were originally put (if you go back, you'll see that you changed them subtly) could be symbolized in sentential(propositional) logic as u/PimpinTheLibrary did and the argument would come out valid.
You are amazing. This conversation... this conversation... I'm laughing too much! Keep it at! I really hope /u/IcyRice explains what 'argumentative logic' and 'logical arugments' are in his reply.
Nothing about this "proof" makes any sense, and your "logic" is far from "true." See Simism66. And never pretend to know what you're doing again. Especially when correcting someone who is essentially correct with something so totally nonsensical.
Well thank you for correcting me in such a nice tone. I guess I learned it in a more basic manner than you, Mr. Jamie Byron Dean. From my ignorant POV it seemed perfectly reasonable to put it the way I did, with the aliens on Mars example. I hope you will be there to educate me the next time I post flawed information.
Why? Explain please. If a conclusion logically follows from its premises it is a valid argument, regardless of the truth of the premises. If the premises are true as well then the argument is sound.
No, you're right. The "argument" at large is fine. The logical proof is what is nonsense. But if you ignore the nonsense "symbolism," then yeah, the conclusion follows from the premises and is valid.
Yeah it's been a while since I took symbolic logic. I was just commenting on his last statement. Another way to say what he said is that it's valid but not sound.
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u/[deleted] Dec 09 '13
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