In this paper we want to stress the relevance of paired fuzzy sets, as already proposed in previous works of the authors, as a family of fuzzy sets that offers a unifying view for different models based upon the opposition of two fuzzy sets, simply allowing the existence of different types of neutrality associated to the different semantic relationships that may hold between opposite references. This scheme should be seen as a basic model for knowledge acquisition, which eventually will lead to a better understanding of the relationship of different knowledge representation models and to the acquisition of more complex valuation scales.