SECTION 6. -THE PROGRESS OF METHODOLOGICAL THEORY. 51 



shall ensure the correctness of our observations ? Is it sufficient 

 to make one observation, or two, or five, or ten? Consider 

 an instance. The inhabitants of Uganda suffer from sleeping 

 sickness, and it is required to ascertain its cause. Some one 

 submits that the Tsetse fly is answerable for the many deaths 

 traceable to this disease. Does it, then, suffice to make one 

 or two observations, and to note the presence of the fly in 

 these cases ? But let us idealise our example, a process not 

 contemplated by Mill. Suppose we learn that everybody in 

 Uganda who is suffering from sleeping sickness has been molested 

 by a Tsetse fly, that no one who has not been so molested 

 has the particular sickness, and that more or fewer Tsetse flies 

 means more or less sleeping sickness, does it follow now that 

 the Tsetse fly is the direct cause of the sleeping sickness? 

 Now, skilful observation has shown that the cause is some 

 species of Trypanosome which, is harboured by the Tsetse fly. 1 

 Unless, therefore, we are absolutely sure with regard to the 

 number of possible causes, and are certain, too, that we have 

 observed correctly, the Canon can never be said to have been 

 truly applied. In other words, Mill was unconscious of the 

 impracticability of dealing with methods of 'proof apart from 

 methods of discovery. 



Finally, the Canons only profess to be concerned with causes. 

 Mill, following Herschel 2 , speaks of "the notion of cause being 

 the root of the whole theory of induction" (Logic, p. 213), and 

 of "inductive inquiry having for its object to ascertain what 

 causes are connected with what effects" (p. 251). Yet in other 

 places he tells us that "induction may be defined the operation 

 of discovering and proving general propositions" (p. 186), that 

 "induction is that operation of the mind by which we infer 

 that what we know to be true in a particular case or cases, 

 will be true in all cases which resemble the former in certain 

 assignable respects" (p. 188), that "induction is a process of 

 inference" (p. 188), and that "induction, properly so-called,... 

 may, then, be summarily defined as Generalisation from Ex- 

 perience" (p. 200). We are confronted here with a palpable 

 contradiction, for we may generalise static facts as we may 

 generalise causes; but the establishment of a cause is not 

 called a generalisation, any more than the establishment of 

 a fact as such. Mill's Canons do not, therefore, propose any 

 tests dealing with generalisation as such, with generalisation as 

 to objects and causes, or with facts as such. 3 



1 In certain parts of Africa the Tsetse fly is not infected, and therefore 

 innocuous. 



2 Herschel, in this matter, followed Bacon, who was evidently following 

 in others' footsteps: "It is a correct position that 'true knowledge is know- 

 ledge by causes'." (Novum Organum, bk. 2, 2.) 



* A spirited attack on the Canons will be found in Bradley's Logic. 

 pp. 331-342. 



4* 



