... subject. It is in this sense that logic is, what it was so expressively called by the schoolmen and by Bacon, ars artium; the science of science itself. All science consists of data and conclusions ... depends on, and the steps of which it consists, is the only basis on which a system of rules, fitted for the direction of the process, can possibly be founded. Art necessarily presupposes knowledge; ... respecting those hidden causes of phenomena, which are named substances and attributes. A substance, however, being to us nothing but either that which causes, or that which is conscious of, ...