 This ecological analogy sheds light on a dispute over the question whether speech acts can profitably be studied in isolation from the conversations in which they occur. An empiricist framework, exemplified in John Stuart Mill’s A System of Logic, suggests attempting to discern the meaning of a word, for instance a proper name, in isolation. By contrast, Gottlob Frege (1884) enjoins us to understand a word’s meaning in terms of the contribution it makes to an entire sentence. Such a method is indispensable for a proper treatment of such expressions as quantifiers, and represents a major advance over empiricist approaches. Yet students of speech acts have espoused going even further, insisting that the unit of significance is not the proposition but the speech act. Vanderveken writes,