THE TYPES OF ARGUMENTS
Normally we classify all arguments into one of two types: deductive and inductive. Deductive arguments are those meant to work because of their pattern alone, so that if the premises are true the conclusion could not be false. All other arguments are considered to be inductive (or just non-deductive), and these are meant to work because of the actual information in the premises so that if the premises are true the conclusion is not likely to be false. The difference is between certainty (we can be sure the conclusion is correct) and probability (we can bet on the conclusion being correct).
We now go one step further. A deductive argument with the right form is considered to be valid, regardless of the truth of the premises. When the premises are in fact true and the argument is valid, then we call it sound.
Inductive arguments can be seen as strong (the conclusion is more likely to be true because of support provided by the premises) or as weak. When an inductively strong argument does have true premises, we call it cogent.
How strong does an argument have to be to be acceptable? A good rule to start with is that the more is at risk, the more likely you want the conclusion to be correct. For instance, in a civil case (the kind that occurs when one person sues another) a jury is asked to decide between two sides based simply on the preponderance of the evidence, and typically there can be a split decision among the jurors. However, in a criminal case there is obviously more at stake (it could be a person's freedom or possibly his life), and so the jury is asked to decide unanimously on the basis of there not being a reasonable doubt about their verdict. In everyday life, you would expect a stronger argument about where to transfer for the last two years of college than you would about what movie to see next weekend.
All arguments then can be classified as valid or invalid. If valid, they are sound or unsound. If...
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