The object of this paper is to provide a systematic treatment of aggregation of individual welfare as a basis for social preference. Two polar cases of interpersonal comparability seem to have received all the attention in the literature so far. Either it is assumed that individual welfare measures are fully comparable, e.g., in Marshall [12], or that they are not comparable at all, e.g., in Robbins [15]. It is clear, however, that we frequently make judgments that are not consistent with noncomparability but which do not require full comparability. Part of the object of this paper is to examine the formal basis of such judgements and to develop a continuum of intermediate assumptions.