_Logic_, as a practical science, studies the mental acts and processes involved in discovering and proving truths and systematizing these into sciences, with a view to directing these acts and processes aright in the accomplishment of this complex task. Hence it has for its subject-matter, in a certain sense, _all_ the data of human experience, or whatever can be an object of human thought. But it studies these data not directly or in themselves or for their own sake, but only in so far as our acts of reason, which form its direct object, are brought to bear upon them. In all the other sciences we employ thought to study the various objects of thought as things, events, realities; and hence these may be called “real” sciences, _scientiae reales_; while in Logic we study thought itself, and even here not speculatively for its own sake or as a reality (as we study it for instance in Psychology), but practically, as a process capable of being directed towards the discovery and proof of truth; and hence in contradistinction to the other sciences as “real,” we call Logic _the_ “rational” science, _scientia rationalis_. Scholastic philosophers express this distinction by saying that while Speculative Philosophy studies _real_ being (_Ens Reale_), or the objects of direct thought (_objecta primae intentionis mentis_), Logic studies the being which is the _product of thought_ (_Ens Rationis_), or objects of reflex thought (_objecta secundae intentionis mentis_).(12) The mental processes involved in the attainment of scientific truth are conception, judgment and inference; moreover these processes have to be exercised methodically by the combined application of analysis and synthesis, or induction and deduction, to the various domains of human experience. All these processes, therefore, and the methods of their application, constitute the proper subject-matter of Logic. It has been more or less a matter of debate since the days of Aristotle whether Logic should be regarded as a department of philosophical science proper, or rather as a preparatory discipline, an instrument or _organon_ of reasoning—as the collection of Aristotle’s own logical treatises was called,—and so as a vestibule or introduction to philosophy. And there is a similar difference of opinion as to whether or not it is advisable to set down Logic as the first department to be studied in the philosophical curriculum. Such doubts arise from differences of view as to the questions to be investigated in Logic, and the point to which such investigations should be carried therein. It is possible to distinguish between a more elementary treatment of thought-processes with the avowedly practical aim of setting forth canons of inference and method which would help and train the mind to reason and investigate correctly; and a more philosophical treatment of those processes with the speculative aim of determining their ultimate