Positive? Negative!

A linguistics professor was expounding upon the differences in positives and negatives in different languages. According to this professor:

  1. In the English language, a double negative makes something positive.
  2. In Russian and some related languages, a double negative remains negative.
  3. And the professor asserted there is no language, however, in which a double positive makes a negative.

When he made this last statement someone in the back of the room piped up "Yeah, right."