When modeling only positive and negative labels for sentiment, negators are generally treated as flipping the polarity of the adjective it modifies (Choi and Cardie, 2008;Nakagawa et al., 2010).
recent work (Taboada et al., 2011;Liu and Seneff, 2009) suggests that the effect of the negator when ordinal sentiment scores are employed is more akin to dampening the adjective's polarity rather than flipping it.