 I’m less than 1% certain that (4). On the contrary, I believe that if Reagan doesn’t win, Carter will win. As these opinions seem sensible, we have a prima facie counterexample to modus ponens: I accept (2) and (3), but reject (4). Truth conditions or not, valid arguments obey the probability-preservation principle. I’m 100% certain that (2), 90% certain that (3), but less than 1% certain that (4).