Current work on lexical collocations uses two ideas: (i) words have distinctive semantic profiles or "prosodies"; and (ii) the strength of association between words can be measured in quantitative terms. These ideas can be combined to provide comparative semantic profiles of words, which show the frequent and characteristic collocates of node words, and make explicit the semantic relations between the collocates.Using data from corpora of up to 120 million words, it is shown that the lemma CAUSE occurs in predominantly "unpleasant" collocations, such as cause of the trouble and cause of death. A case study of this lemma is used to illustrate quantitative methods for investigating collocations. Various methods proposed in the literature are of great practical value in establishing collocational sets, but their theoretical basis is less clear. Brief comparative semantic profiles are given for related lemmas, e.g. REASON and CONSEQUENCE. Implications for the relation between system and use are discussed.