I think Sentiment built-in classifier is for regular English use. Are you trying to check Sentiment or convoluted logic? Even if you train your classifier to be better at a bit logically convoluted statements, then you can always make them even more logically confusing and the classifier would fail again. But then it would not be really a regular-life English at all. So you have to figure out what you really need. Sentiment built-in classifier works great with most sentences in regular every-day English. It cannot be trained, I think. If you need some other type of English you can train Classify function as shown in many examples in docs.