368 SPAEKS FROM A GEOLOGIST'S HAMMER. 



This conclusion cannot be avoided. The reality and 

 gemiineness of our knowledge of the phenomena assumed 

 as the material of science is absolutely conditioned on the 

 veracity of consciousness in certain of its testimony. Im- 

 pugn this veracity in any respect, and the genuineness of 

 the materials of science is correspondingly impaired. The 

 more valiantly we affirm the indestructibility of scientific 

 knowledge, the more explicitly we admit the unimpeach- 

 able veracity of the testimony of consciousness. If con- 

 sciousness is not admitted as a veracious witness thus far, 

 it is impossible to hold an argument with the reader. If 

 consciousness is admitted veracious, so far as to validate 

 the phenomena from which science proceeds, we may next 

 inquire what are the further implications of scientific 

 knowledge. 



III. Supposing the facts of observation to stand in 

 every respect unchallenged, some principles of relation 

 must be tacitly assumed to serve as the ground and au- 

 thentication of any classification. Whether we associate 

 them with reference to time or place, concomitance or 

 succession, quantity or quality, it is in every case a basis 

 of resemblance. Without some kind of mutual resem- 

 blance, no homogeneity or community would be present 

 to justify any general predication. But when we adopt 

 any kind of resemblance as the basis of classification, we 

 tacitly assume that likeness among phenomena proceeds 

 from community or identity of cause ; in other words, 

 that " like effects proceed from like causes." This is a 

 principle which must be validated by pure reason to ac- 

 quire that character of certainty, universality and necessity 

 which we assume it to possess in the use which we make 

 of it. If it be thought a principle resting on a general 



