Self-study
What do we do when there are two conditional indicators? For example:
No student is chosen for Gryffindor unless they exhibit bravery. Therefore, if a student exhibits bravery, they will be sorted to Gryffindor. Lawgic:
A → B
B → A
The argument is invalid.
How come it is not /chosen->/exhibit bravery? indicator “no” and indicator “unless” make negate sufficient condition and negate necessary condition. If we create the contrapositive it makes brave-> chosen which matches the second sentence.
Ah you are awesome, I think I am seeing some light in the fog. I didn't think of this as an exception. If we don't think about the exceptions, both "no" and "unless" are conditional indicators. So what I was saying is by the conditional indicator rules you can pick one key term and negate it and turn it into the sufficient one (for unless) and pick the other key term negate it and put it in the necessary position respectively (for no).