 As a philosopher with a mathematical background, Husserl was interested in developing a general theory of inferential systems, which (following Bolzano) he conceived of as a theory of science, on the ground that every science (including mathematics) can be looked upon as a system of propositions that are interconnected by a set of inferential and grounding relations. Following John S. Mill, he argues in Logical Investigations that the best way to study the nature of such propositional systems is to start with their linguistic manifestations, i.e., (sets of) sentences and (assertive) utterances thereof.