syllogisms
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Original Question
Is this syllogism valid or invalid?
Violent television influences some children in negative ways. Some children are violent. Some children are influenced by violent television.
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Answers
1Hi, Deborah!
The argument is valid for just the reason that Dr. Bennett gave. An argument is valid just in case it is impossible that every premise is true but the conclusion false. It is impossible that every premise of the argument you gave is true but the conclusion false, especially, as Dr. Bennett has said, because the premises of the argument include the statement that is in the conclusion!
As a side note, in logic a tautology is a kind of sentence or statement, rather than an argument. So, tautologies are neither valid nor invalid. However, most valid arguments of our experience can be converted into a tautology by making the argument into a conditional (which is a kind of sentence or statement). To do this, conjunct the premises of the argument and make them the antecedent. Take the conclusion of the argument and make it the consequent. This conditional will be a tautology (this means that when the conditional is run through a truth table, the last column of the truth table will contain only T s ("T" stands for "true"), which is to say the conditional is true in every valuation. And a sentence that is true in every valuation is a tautology.)
As for whether the argument is a valid syllogism , my humble opinion is no. Why? Well, irrelevant premises do not affect the validity of the argument, so they are safe to remove. And if the irrelevant premise is false, then the argument is unsound because it does contain a false premise. In a word, removing the irrelevant premise does not harm the argument, but keeping it potentially does harm the argument (at least if the premise is not necessarily true). So, when evaluating the argument, the principle of charity says go ahead and remove the irrelevant premise for good measure. Dr. Bennett indicated this to you when he crossed out the second premise, and I agree with that move. But since the premise is removed in order to charitably evaluate the argument, and since it was after all the second premise, the argument has only one premise when it is evaluated. So, the argument is not evaluated as a syllogism . For this reason, I say no: when I evaluate the argument, I find that it is valid, but I do not find it valid as a syllogism. Though this is an interesting issue and I welcome disagreement.
Thank you, Deborah.
From, Kaiden
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P1. Violent television influences some children in negative ways.
P2. Some children are violent.
C. Some children are influenced by violent television.
The conclusion is just a restatement of the first premise. This is a tautology. As for being a "valid syllogism," I think I will defer to some of the members who specialize in formal logical and syllogisms. Academically, I am not sure if such a tautology would be considered valid or not. Technically, if P1 is true the conclusion must be true as well, but given the structure, I am not sure if this would even be considered a syllogism.
Ben and Jerry's influences the size of my gut by making it bigger.
Irrelevant stuff here.
The size of my gut is influenced by Ben and Jerry's.