Classic(al) Rock

One of the syllogisms Boy-A-Thon had to write in Logic class today was a modus tollens. This syllogism follows the pattern:

If P, then Q.
Not Q.
Therefore, not P.

His work:

If I'm back in black, I'll hit the sack.
I won't hit the sack.
Therefore, I'm not back in black.

I love my job!