Right.
But , uh , the problem is , training sets aren't perfect and testing sets are different. So you f you  you face the potential problem with discriminative stuff , be it LDA or neural nets , that you are training to discriminate between categories in one space but what you 're really gonna be g getting is  is something else.
Uh - huh.
And so , uh , Stephane 's idea was , uh , let 's feed , uh , both this discriminatively trained thing and something that 's not. So you have a good set of features that everybody 's worked really hard to make ,