Strong and Weak Arguments

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There are two importantly different ways in which an argument can satisfy the Logic Condition. One way is if the argument is VALID. Another way is if the argument is STRONG. We've talked about validity. Now let's talk about strength. Here's an argument: 1. All humans have DNA. 2. Pat is human. Therefore, Pat has DNA.
 
This is a valid argument. If the premises are true the conclusion can't possibly be false. Now take a look at this argument: 
1. 50% of humans are female. 2. Pat is human. Therefore, Pat is female. 
 
The percentage isn't exact, but we're not interested in whether the premises are actually true. We're interested in whether, if they were true, the conclusion would follow. In this case the answer is clearly NO. Knowing that Pat is human doesn't give any good reason to think that he or she is female. This is an example of an argument that does NOT satisfy the Logic Condition. Now take a look at this argument: 
1. 90% of humans are right-handed. 2. Pat is human. Therefore, Pat is right-handed. 
 This argument is different. In this case the premises make it very likely — 90% likely — that the conclusion is true. They don't guarantee that Pat is right-handed, but we might still want to say that they provide good reasons to think that Pat is right-handed. And if that's the case then we should say that this argument satisfies the Logic Condition. Because it has the property that, if all the premises are true, they give us good reason to believe the conclusion. This difference is what the distinction between weak and strong arguments amounts to. The first argument is what we call a logically WEAK argument. It does not satisfy the Logic Condition and so it can't be a good argument. The second argument is a logically STRONG argument. It does satisfy the Logic Condition so it can be a good argument.
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