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Monday, March 09, 2015


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"But I am loath to say that the argument (as opposed to the just-depicted argument-form) is invalid. It strikes me as valid. But how could it be valid?"

I am not sure why you would be loath to say the argument is invalid. Just because the conclusion and all the premises are true that does not mean the argument is valid.

Interestingly, enough I think premise 1.5 could be false. For example even if there were just one man, and he was not an angel there would still be no need for government.

"Might it be that 'if ___ then ___' sentences in English sometimes express biconditional propositions? Clearly, if we replace (1) with

1* Men are angels if and only no government is necessary

the resulting argument is valid."

I think people do this quite a bit, but I can't think of examples right now. On LSAT tests they usually have a critical reasoning question that involves denying the antecedent. I suspect some people never get that one right.

You must not read this blog, else you would not have suggested that I think that the validity of an argument follows from its having true premises and conclusion.

To evaluate a stretch of argumentative prose, one must do two things. First, identify the argument. Second, identify the logical form of the argument you have identified.

Now someone who gives the (1)-(3) argument is charitably interpreted as arguing something like the following:

Whether or not government is needed depends on whether or not men are morally perfect. If they are, then they do not need government. If they are not, then they do. Now men are not morally perfect. Therefore, they need government.

This argument is plainly valid.

So the original argument cannot be reasonably dismissed as denying the antecedent; it is more reasonably understood as an enthymeme which, when the tacit premises are added, is valid.

Compare the last argument I cited, which cannot be given a charitable reading.

You're right that there is no need for government on Robinson Crusoe's island. But of course Madison was not talking about that situation, nor was he talking about a situation in which a few people who love one another live together.

To understand my analysis you must realize that a one and the same sentence can be used to express different propositions, and that an argument is a sequence of propositions, not of sentences.

I see what you mean. Sometimes the hidden assumption is also true, so plugging it in is not a problem. Some things can be assumed and need not be stated.

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