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tion. It was he who noted that the kind of know- 

 ledge accesssible to science is that which is useful for 

 the guidance of action, and he laid much stress on 

 this, although it was of course impossible for him to 

 see the importance of the fact in its bearing upon 

 evolution. Hume (1711-1776) accepted the position 

 of Hobbes and Locke that knowledge originates 

 through sense impressions, as being the best which 

 was available at the time ; but he showed that no 

 completely intelligible and consistent syntax of the 

 genesis of knowledge was possible, even on this basis, 

 so long as it was associated with the psychological 

 theory then current. The theory was that each 

 momentary sense impression should be regarded as 

 an isolated unit having no organic connection with 

 any previous impression ; and Hume saw clearly that 

 no mere collection of such isolated units could con- 

 stitute knowledge. His predecessors had been more 

 or less aware of this also, and had tried to supply 

 what I may call metaphysical connections between 

 the separate units ; he examined these connections 

 and found them unintelligible, or to use his own term 

 " irrational." Owing to the current misconception of 

 the nature of science, and to the rudimentary condi- 

 tion of physiology at the time it was not open to 

 Hume to adopt a more consistent psychological 

 theory ; all he could do was to point out the diffi- 

 culties, and to adopt an attitude of scepticism, or 

 suspended judgment, till the means of overcoming them 



