4 NATURE AND DESIGN OF THIS WORK. [CHAP. I. 



The general laws of Nature are not, for the most part, imme- 

 diate objects of perception. They are either inductive inferences 

 from a large body of facts, the common truth in which they ex- 

 press, or, in their origin at least, physical hypotheses of a causal 

 nature serving to explain phenomena with undeviating precision, 

 and to enable us to predict new combinations of them. They 

 are in all cases, and in the strictest sense of the term, probable 

 conclusions, approaching, indeed, ever and ever nearer to cer- 

 tainty, as they receive more and more of the confirmation of ex- 

 perience. But of the character of probability, in the strict and 

 proper sense of that term, they are never wholly divested. On the 

 other hand, the knowledge of the laws of the mind does not require 

 as its basis any extensive collection of observations. The general 

 truth is seen in the particular instance, and it is not confirmed 

 by the repetition of instances. We may illustrate this position 

 by an obvious example. It may be a question whether that for- 

 mula of reasoning, which is called the dictum of Aristotle, de omni 

 et nullo, expresses a primary law of human reasoning or not ; but 

 it is no question that it expresses a general truth in Logic. Now 

 that truth is made manifest in all its generality by reflection 

 upon a single instance of its application. And this is both an 

 evidence that the particular principle or formula in question is 

 founded upon some general law or laws of the mind, and an illus- 

 tration of the doctrine that the perception of such general truths 

 is not derived from an induction from many instances, but is in- 

 volved in the clear apprehension of a single instance. In con- 

 nexion with this truth is seen the not less important one that 

 our knowledge of the laws upon which the science of the intellec- 

 tual powers rests, whatever may be its extent or its deficiency, is 

 not probable knowledge. For we not only see in the particular 

 example the general truth, but we see it also as a certain truth, 

 a truth, our confidence in which will not continue to increase 

 with increasing experience of its practical verifications. 



5. But if the general truths of Logic are of such a nature that 

 when presented to the mind they at once command assent, 

 wherein consists the difficulty of constructing the Science of 

 Logic ? Not, it may be answered, in collecting the materials of 

 knowledge, but in discriminating their nature, and determining 



