Results 1 to 4 of 4

Math Help - Valid or Invalid Arguments

  1. #1
    Newbie
    Joined
    Apr 2008
    Posts
    2

    Red face Valid or Invalid Arguments

    Very confused about valid or invalid arguments and knowing when and when not to construct truth tables or when to use the standard form for example:
    I understand how to construct tables for example for p, q, r. Confused on how to present the argument.

    Problem:
    p v q
    ~q
    therefore P

    Assistance is greatly appreciated and needed.

    gperson
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member Aryth's Avatar
    Joined
    Feb 2007
    From
    USA
    Posts
    652
    Thanks
    2
    Awards
    1
    When determining the validity of this argument, you can use a truth table. But you can also use an explanation of it to a certain extent to where the validity of the argument is stated or implied.

    We have p or q. And we have to assume not q and therefore get p.

    1. p v q hyp
    2. ~q hyp
    3. p 1, 2, disjunctive syllogism

    Roughly speaking, using the or connective, we are told that at least one of the statements is true, and then we are told that q is not true, so we can infer that the p must be true.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Super Member

    Joined
    May 2006
    From
    Lexington, MA (USA)
    Posts
    11,659
    Thanks
    600
    Hello, gperson!


    p v q
    . ~q
    -----
    . p

    The argument is: . \bigg[(p \vee q) \:\wedge \sim q\bigg] \;\to \;\;\sim q


    The truth table looks like this:

    . . \begin{array}{|c|c|ccccccc}<br />
p & q & [(p & \vee & q) & \wedge & \sim q] & \to & p \\ \hline<br />
T & T & T & T & T & F & F & {\color{blue}T} & T \\<br />
T & F & T & T & F & T & T & {\color{blue}T} & T \\<br />
F & T & F & T & T & F & F & {\color{blue}T} & F \\<br />
F & F & F & F & F & F & T & {\color{blue}T} & F \\ \hline<br />
& & _1 & _2 & _1 & _3 & _1 & _4 & _1<br />
\end{array}

    Follow Math Help Forum on Facebook and Google+

  4. #4
    Newbie
    Joined
    Apr 2008
    Posts
    2

    Arguments & Truth Tables

    Thanks Aryth as this is very helpful. I am still learning how to use the various arguments and it can get quite confusing. Your help is greatly appreciated and needed. Your directions were easier to understand than many web sites I visited for clarity. Clear directions make a difference.

    I have other types of arguments that I am trying to work on and it is confusing to me.

    Again, I really appreicate your assistance

    gperson
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. How do I know if an argument is valid or invalid?
    Posted in the Discrete Math Forum
    Replies: 5
    Last Post: November 24th 2011, 05:41 PM
  2. IS this proof valid or invalid?
    Posted in the Number Theory Forum
    Replies: 5
    Last Post: August 9th 2011, 01:48 PM
  3. Determine whether these are valid arguments
    Posted in the Discrete Math Forum
    Replies: 3
    Last Post: September 27th 2010, 12:21 AM
  4. valid or invalid argument?
    Posted in the Discrete Math Forum
    Replies: 2
    Last Post: July 2nd 2009, 02:54 PM
  5. valid or invalid ?
    Posted in the Discrete Math Forum
    Replies: 2
    Last Post: October 20th 2007, 09:55 AM

Search Tags


/mathhelpforum @mathhelpforum