  There has been a growing interest, both in physics and psychology, in
understanding contextuality in experimentally observed quantities. Different
approaches have been proposed to deal with contextual systems, and a promising
one is contextuality-by-default, put forth by Dzhafarov and Kujala. The goal of
this paper is to present a tutorial on a different approach: negative
probabilities. We do so by presenting the overall theory of negative
probabilities in a way that is consistent with contextuality-by-default and by
examining with this theory some simple examples where contextuality appears,
both in physics and psychology.
