Students breaking vending machines

I was also told in elementary school that you can't start a sentence with the word because. Because of this, I highly doubt 100% of everything they say is correct. Dumber is not improper English. If it was, then why wouldn't the word 'smarter' be?

Smart - Smarter - Smartest

Dumb - Dumber - Dumbest

Example: "My cat is smarter than your cat." "No kidding. He's dumber than a sack of potatoes."

Stupider is not a word. That might be what you're remembering.

 

I was never sure so I always tried to stay away from that word in speech and writing. Part of growing old is finding out the people you immortalized were wrong. Even some of my professors were wrong.