> I remember thinking how on earth did Porter get his name on a "theory" when really that's just common sense?
This is how I've always felt about "De Morgan's Laws". There are two, and they state:
1. If it is not the case that two things are both true, then at least one of those things is false.
2. If it is not the case that either of two things is true, then both of those things are false.
(Actually, they are logical equivalences, so they also apply in the other order -- "1b. If at least one of two things is false, then it is not the case that both things are true.")
I'm pretty sure both of those "laws" were known well before the nineteenth century.
This is how I've always felt about "De Morgan's Laws". There are two, and they state:
1. If it is not the case that two things are both true, then at least one of those things is false.
2. If it is not the case that either of two things is true, then both of those things are false.
(Actually, they are logical equivalences, so they also apply in the other order -- "1b. If at least one of two things is false, then it is not the case that both things are true.")
I'm pretty sure both of those "laws" were known well before the nineteenth century.