Errors In The Structure Of Argument
1) An error in argument structure generates problems. It permits false conclusions from true premises. Also, it hides viable alternatives. Faulty arguments do not connect conclusions with the evidence (the premises) offered for them. If the conclusion happens to be true, it is accidental, so far as the premises are concerned.
2) Many people can recognize that the a-examples below are wrong. But when the same faulty structure contains terms that affect them emotionally, see the b-examples, they tend to miss the structural error.
b. Sam reads Karl Marx, so he must be a communist because Communists read Karl Marx.
The viable alternatives overlooked in these two examples are --: for a: things that are fruits do not all have to be oranges. For b: non-communists, even anti-communists may read Karl Marx.
a. All dogs are warm-blooded. Your pet is warm-blooded. So it must be a dog.
Possible missed alternative: your pet is a cat and also warm-blooded, since all cats are.
b. John must be a businessman, since businessmen support immigration and so does John.
Possible missed alternative: John may be a school teacher who supports immigration.
b. Some businessmen support unrestricted immigration. John is a businessman, so he must support unrestricted immigration.
b. Since union members oppose unrestricted immigration and John is not a union member, he does not oppose unrestricted immigration.
b. John supports unrestricted immigration but he's a jerk!
b. "Liberalism destroys!" my uncle Rush, the famous statistician, always says.