[sanxiyn]

If you think about it, this can't be otherwise. Positive/negative is misleading, since that distinction is the entire thing we are trying to teach. Let's call two labels A and B. You tell the model:

This long penis is A. This short penis is A. This cat is B. This dog is B. Now, what is this ceiling?

The model, looking at the ceiling, discovers a long fluorescent tube. It is long! Neither cat nor dog is long (The model is yet to discover longcat), and while penis comes in long and short variety, all penises seem long-ish. The ceiling is A.