Part 4: Arguments that make sense
Deductive reasoning: Is either true or false
Arguments can be separated into two categories: deductive and inductive. A deductive argument is one in which it is impossible for the premises to be true but the conclusion false. Thus, the conclusion follows necessarily from the premises and inferences. In this way, it is supposed to be a definitive proof of the truth of the claim (conclusion). Here is a classic example:
1. All men are mortal. (premise)
2. Socrates was a man. (premise)
3. Socrates was mortal. (conclusion)
As you can see, if the premises are true (and they are), then it simply isn't possible for the conclusion to be false.
Arguments that make sense
Inductive reasoning: is probably true
An inductive argument is one in which the premises are supposed to support the conclusion in such a way that if the premises are true, it is improbable that the conclusion would be false. Thus, the conclusion follows probably from the premises and inferences. Here is an example:
1. Socrates was Greek. (premise)
2. Most Greeks eat fish. (premise)
3. Socrates ate fish. (conclusion)
In this example, even if both premises are true, it is still possible for the conclusion to be false (maybe Socrates was allergic to fish, for example). Words which tend to mark an argument as inductive — and hence probabilistic rather than necessary — include probably, likely, possibly and reasonably.