204 OPERATIONS SUBSIDIARY TO INDUCTION. 



ral feeling that they resemble, without having analysed their 

 resemblance, or perceived in what points it consists, and fixed 

 in our memory an exact recollection of those points. This 

 want of clearness, or, as it may be otherwise called, this vague- 

 ness, in the general conception, may be owing either to our 

 having no accurate knowledge of the objects themselves, or 

 merely to our not having carefully compared them. Thus a 

 person may have no clear idea of a ship because he has never 

 seen one, or because he remembers but little, and that faintly, 

 of what he has seen. Or he may have a perfect knowledge 

 and remembrance of many ships of various kinds, frigates 

 among the rest, but he may have no clear but only a confused 

 idea of a frigate, because he has never been told, and has not 

 compared them sufficiently to have remarked and remembered, 

 in what particular points a frigate differs from some other kind 

 of ship. 



It is not, however, necessary, in order to have clear ideas, 

 that we should know all the common properties of the things 

 which we class together. That would be to have our con- 

 ception of the class complete as well as clear. It is sufficient 

 if we never class things together without knowing exactly 

 why we do so, without having ascertained exactly what 

 agreements we are about to include in our conception ; and if, 

 after having thus fixed our conception, we never vary from it, 

 never include in the class anything which has not those 

 common properties, nor exclude from it anything which has. 

 A clear conception means a determinate conception ; one 

 which does not fluctuate, which is not one thing to-day and 

 another to-morrow, but remains fixed and invariable, except 

 when, from the progress of our knowledge, or the correction 

 of some error, we consciously add to it or alter it. A person 

 of clear ideas, is a person who always knows in virtue of what 

 properties his classes are constituted; what attributes are 

 connoted by his general names. 



The principal requisites, therefore, of clear conceptions, are 

 habits of attentive observation, an extensive experience, and a 

 memory which receives and retains an exact image of what is 

 observed. And in proportion as any one has the habit of 



