OF REASON AND SENSATION. 263 



or proposition of any kind. By habit the mind does these operations with 

 ease, and often goes on doing them almost without being conscious of it. 



I believe that the will has no hand in any of the operations of an animal 

 respecting the machine itself; but it is and can be employed in the 

 operations that respect foreign matter. 



Reasoning is fallacious if not based upon facts ; but facts and reason- 

 ing should go hand in hand ; for if the facts are not able to support the 

 reasoning, then the reasoning is good for nothing : they should always 

 bear a due proportion. If the facts overbalance the reasoning, and it 

 requires a load of facts to give us a competent knowledge of anything, 

 then they [facts or teachers] become dull and heavy. 



The man who judges from general principles only, shows ignorance : 

 few things are so simple as to come wholly within a general principle. 



"We should never reason on general principles only, much less practise 

 upon them, when we are, or can be, master of all the facts ; but, where 

 we have nothing else but the general principle, then we must take it 

 for our guide. 



On Ideas from Sensation. 



Perhaps sounds are the most simple sensations we have ; for when a 

 single body gives a sound, we do not know whether it is a simple sound 

 or a combination of sounds. We suppose it simple, because we are not 

 yet able to make any separation of the sensation ; and by combination 

 we are not able to bring out any sounds like those that are produced 

 from the most simple percussion. Until Sir Isaac Newton separated the 

 rays of light, white was supposed to be a simple colour. A body is of 

 no colour when there is no light. 



High or low sounds depend on the number of vibrations. Difference 

 in sounds of the same height depends on the smooth or soft, and vice versa 

 of their motions. 



"We certainly know whence sounds come fr©m habit, or by the intelli- 

 gence of our other senses, as we know that there is something external 

 that produces it. 



The reason why we cannot tell or know what heat is, is because it is 

 only capable of affecting one sensation, and that only in one way. 

 Of bodies that are more gross, and capable of affecting the senses in 

 more ways than one, and more than one sense, we can form an idea of 

 their manner of action. 



No man can have any idea of extension at first ; his notion must come 

 by degrees ; the same thing must be repeated again and again ; and the 

 sensation that the notion of extension arises from, must become fami- 

 liar : it is from motion in our bodies at first, joined with feeling, that 

 we judge of extension or space ; then time is compounded with it. 



