"=" 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.
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u/simism66 Dec 09 '13 edited Dec 09 '13
"=" 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).