DEFINITION AND PROVINCE OF LOGIC. 21 



what part is constructed out of materials furnished to it from without. To 

 this science appertain the great and much debated questions of the exist- 

 once of matter ; the existence of spirit, and of a distinction between it and 

 matter ; the reaUty of time and space, as things without the mind, and 

 distinguishable from the objects which are said to exist in them. For 

 in the present state of the discussion on these topics, it is almost uni- 

 versally allowed that the existence of matter or of spirit, of space or of 

 time, is in its nature unsusceptible of being proved ; and that if any thing 

 is known of them, it must be by immediate intuition. To the same science 

 belong the inquiries into the nature of Conception, Perception, Memory, 

 and Belief ; all of which are operations of the understanding in the pursuit 

 of truth ; but with which, as phenomena of the mind, or with the possibili- 

 ty which may or may not exist of analyzing any of them into simpler phe- 

 nomena, the logician as such has no concern. To this science must also be 

 referred the following, and all analogous questions : To what extent our in- 

 tellectual faculties and our emotions are innate — to what extent the result 

 of association : Whether God and duty are realities, the existence of which 

 io manifest to us a priori by the constitution of our rational faculty ; or 

 whether our ideas of them are acquired notions, the origin of which we 

 are able to trace and explain ; and the reality of the objects themselves a 

 question not of consciousness or intuition, but of evidence and reasoning. 



The province of logic must be restricted to that portion of our knowl- 

 edge which consists of inferences from truths previously known ; whether 

 those antecedent data be general propositions, or particular observations 

 and perceptions. Logic is not the science of Belief, but the science of 

 Proof, or Evidence. In so far as belief professes to be founded on proof, 

 the office of logic is to supply a test for ascertaining whether or not the be- 

 lief is well grounded. With the claims which any proposition has to be- 

 lief on the evidence of consciousness — that is, without evidence in the 

 proper sense of the word — logic has nothing to do. 



§ 5. By far the greatest portion of our knowledge, whether of general 

 truths or of particular facts, being avow^edly matter of inference, nearly the 

 whole, not only of science, but of human conduct, is amenable to the au- 

 thority of logic. To draw inferences has been said to be the great business 

 of life. Every one has daily, hourly, and momentary need of ascertaining 

 facts which he has not directly observed ; not from any general purpose of 

 adding to his stock of knowledge, but because the facts themselves are of 

 importance to his interests or to his occupations. The business of the 

 magistrate, of the military commander, of the navigator, of the physician, 

 of the agriculturist, is merely to judge of evidence, and to act accordingly. 

 They all have to ascertain certain facts, in order that they may afterward 

 apply certain rules, either devised by themselves or prescribed for their 

 guidance by others ; and as they do this well or ill, so they discharge well 

 or ill the duties of their several callings. It is the only occupation in which 

 the mind never ceases to be engaged ; and is the subject, not of logic, but 

 of knowledge in general. 



Logic, however, is not the same thing Avith knowledge, though the field 

 of logic is co-extensive with the field of knowledge. Logic is the com- 

 mon judge and arbiter of all particular investigations. It does not under- 

 take to find evidence, but to determine whether it has been found. Logic 

 neither observes, nor invents, nor discovers;^ but judges. It is no part of 

 the business of logic to inform the surgeon what ap[)earances are found to 



