About
Howdy, stranger.
Welcome to Modus Dopens, wherein are collected my uncensored musings on politics, life, and everything. I used to blog over at The Soapbox, wherein are collected the archives.
Want to drop me a line? I’m at irration_point [at] yahoo [dot] co [dot] uk.
So why “Modus Dopens”?
I’m glad you asked.
As any logic student knows, there are some argument forms in propositional logic that one sees again and again.
- Modus ponens:
If P then Q, P. Therefore, Q.
Formally: P → Q, P ∴ Q - Modus tollens
If P then Q, not Q. Therefore not P.
Formally: P → Q, ~Q ∴ ~P
Both modus ponens and modus tollens are valid argument forms in propositional logic.
The third argument form is modus dopens, which earns its name through being both invalid and commonly mistaken for valid.
If P then Q, not P. Therefore not Q.
Formally: : P → Q, ~P ∴ ~Q
–IP
